Industrial seal self study guide

Transcription

Industrial seal
self study guide
Maximizing radial shaft seal performance.
TABLE OF CONTENTS
Chapter 1
Introduction. . . . . . . . . . . . . . . . . . . . . . . . 2-4
Wear Sleeves . . . . . . . . . . . . . . . . . 53-57
Chapter 6 Review. . . . . . . . . . . . . . . . . 58-59
Basic Seal Types . . . . . . . . . . . . . . . . . 5-9
Chapter 2 Review. . . . . . . . . . . . . . . . . 10-11
Shaft and Bore Conditions . . . . . . . 60-64
Chapter 7 Review. . . . . . . . . . . . . . . . . 65-66
Seal Design Groups . . . . . . . . . . . . . 12-28
Chapter 3 Review. . . . . . . . . . . . . . . . . 29-31
Installation . . . . . . . . . . . . . . . . . . . 67-75
Chapter 8 Review. . . . . . . . . . . . . . . . . 76-77
Seal Applications . . . . . . . . . . . . . . . 32-43
Chapter 4 Review. . . . . . . . . . . . . . . . . 44-45
Troubleshooting . . . . . . . . . . . . . . . 78-84
Chapter 9 Review. . . . . . . . . . . . . . . . . 85-86
Seal Selection . . . . . . . . . . . . . . . . . 46-50
Chapter 5 Review. . . . . . . . . . . . . . . . . 51-52
Glossar y of Seal Terms . . . . . . . . . . 87-93
Final Review . . . . . . . . . . . . . . . . . 94-107
1
CHAPTER 1—
INTRODUCTION
This book, produced for use by distributors and end-users, should
prove of practical value to engineers, industrial designers, maintenance
superintendents and anyone who can benefit from a thorough
understanding of seals.
It will explain:
• What types of seals are available
• How to select the best seal for any given application
• How to improve performance with proper installation
• How to repair seal-worn shaft surfaces
• How to spot and correct seal problems economically
How to Use this Study Guide
This self-study guide is designed to increase performance productivity.
Each chapter consists of a logical organization of material, technical
diagrams and a short quiz to help you retain what you study.
Carefully read the text portion of each chapter. Make notes or
underline if you wish; this can help you remember what you’ve read.
This material is designed for the individual’s own learning pace. At the
end of the program, you will have learned the same information and
should retain it as well as any other “student.”
The chapter quizzes are an important phase of self-study learning
since they are intended to reinforce the material covered. The quiz
questions are straightforward multiple choice and true–false. There
are no “trick questions.” Your answers can easily be checked by
referring to the material presented in the chapter.
Complete each review in order before going on to the next chapter.
If you are not sure of an answer to a question, check back in the
chapter and review that portion again.
If you follow this procedure through all nine chapters, you should
gain a thorough understanding of shaft seals.
You will be able to test your knowledge through an overall “Final
Review” at the end of the book. This is a final check for the reader.
A “Certificate of Merit” to those who successfully pass the final review
with a minimum score of 85% will be issued. Instructions for obtaining
a certificate are at the end of this book.
2
1
Brief Histor y of the Shaft Seal
SKF Sealing Solutions invented and patented the first integrated,
self-contained shaft seal in 1928 (fig. 1a). It was designed to hold
grease in automobile wheel hubs and help lubricate the wheel bearing.
In the mid 1930’s, SKF pioneered the development of custom
formulating, compounding and molding of elastomers (synthetic
rubber) to develop higher performance materials. This led to other
innovations in manufacturing processes, new sealing techniques to
handle more demanding automotive and industrial applications
and the compounding and molding of various elastomer seals to
improve consistency and quality.
SKF invented the shaft
seal in 1928 (fig. 1a).
Today, SKF is the world’s leading supplier of fluid sealing devices for
the truck, automotive, farm equipment, aircraft, heavy machinery
and machine tool industries. SKF also supplies seals for aerospace
missiles, earthmoving equipment, appliances, and a wide variety of
pumps, hydraulic systems, motors and sub-assemblies.
A company-wide commitment to quality earned SKF Sealing
Solutions significant certifications including TS16949 in December
2002 and ISO 9001:2000 in May 1999.
SKF can supply more than 200 types of seals, over 3,000 stock
sizes, and over 10,000 cataloged variations. That includes seals in
both inch and metric sizes, metal and rubber O.D.’s in both bonded
and assembled designs, with single or double lip elements and with
or without springs or inner cases (fig. 1b).
SKF sealing products fit shaft diameters from . 110” to over 180”.
They fit metric shaft diameters from 3mm to over 4572mm. All are
fashioned from an ever-growing spectrum of sealing elements
and materials including LongLife™ fluoroelastomer lip materials.*
That, plus ongoing development of new materials and processes,
will enable SKF to meet tomorrow’s expectations.
Over 2 types of seals are now
available from SKF (fig. 1b).
*LongLife is a registered trademark of SKF
3
INTRODUCTION (cont.)
The Total Bearing and Seal Ser vice Concept
When bearings fail, they can bring equipment to an unscheduled halt.
Every hour of downtime due to premature bearing failure can result in
costly lost production, especially in capital intensive manufacturing.
The majority of bearings outlive the machinery or equipment in
which they are installed. Of the bearings that do fail, only 1/3 fail due
to normal fatigue. Over half of bearing failures result from lubrication
or contamination problems—both of which can be related to the sealing
arrangement. Seals are vital to all bearing applications and are a critical
component in an integrated systems approach to Trouble-Free
Operation.
Product Quali ty
The SKF goal is to provide every bearing user with long, trouble-free
operation. Our substantial investment in research and development has
resulted in the production of bearings and seals of the highest quality.
However, quality alone cannot guarantee trouble-free operation.
Other factors affect the life span of every bearing, including:
Operating Environment
Machinery must be kept in peak operating condition. The bearings should
be properly aligned and protected from extreme temperatures and properly
sealed from moisture and contaminants. The seals must also retain the
lubricant to assure a proper oil film.
Proper Installation
Knowledge of the proper installation techniques and tools is required
to ensure that the bearings and seals are not damaged.
Proper Maintenance
Following lubrication and maintenance schedules and monitoring bearing
operating conditions are also important in maximizing bearing life.
Trouble-Free Operation
SKF is committed to the proper servicing and maintenance of the
bearing/sealing arrangement. The Trouble-Free Operation Concept
minimizes the risk of bearing downtime and ensures that your bearings
achieve their full potential. A full line of products and services is available
from SKF to make installation and maintenance easy to perform.
The Trouble-Free Operation Concept meets customer demands for
long bearing life and cost-effective operation.
4
Chapter 2—Basic Seal Types
Seal Functions
2
Whenever a shaft rotates, it needs a bearing arrangement for smooth,
effective operation. Wherever there’s a bearing, you’ll find a seal helping it to reach its maximum service life and reliability. In simplest terms
a shaft seal is a barrier.
This barrier has four functions:
• Retain lubricants and/or liquids
• Exclude dirt/contaminants
• Separate fluids
• Confine pressure
When a seal performs these functions properly, it protects the bearing
from harmful contaminants while retaining a clean lubricant supply,
resulting in lengthened bearing service life and reliability. The bearings
do their job better, cleanliness of production and process materials is
maintained, lubricant is saved and machinery downtime is reduced.
An integrated bearing/seal system approach is the best way to achieve
trouble-free operation (fig. 2a).
Sealing takes place as lube is
retained and outside contaminants
are excluded (fig. 2a).
Seals handle a broad range of media, from light oil to heavy grease to
hot turbine gases. Electric motors and gear reduction units are some
of the more common applications, however there are extremes requiring very special solutions.
For example, seals protect the high speed turbine pump in a rocket
that accelerates from 0 to 12,000 rpm in one-fourth of a second.
Other types of seals protect the drive unit in a track type earth mover,
operating at only 15 to 30 rpm.
Static Seals
The function of static seals is to create barriers between relatively
non-moving surfaces. Typical “static” applications of seals are
valve-cover gaskets, cylinder covers, packings of many kinds, and
o-rings used in stationary situations. The gasket lining a refrigerator
door used to seal the inside chilled air from the outside ambient
temperature is a classic static seal application. “Static” simply means
that no relative motion takes place in the performance of the sealing
function. The sealing devices for such applications are often tailored
from o-rings. Typical sectional views of static seal applications are
shown in figure 2b.
Sectional views of typical
static or non-moving seal
applications (fig. 2b).
5
BASIC SEAL TYPES (cont.)
Dynamic “Radial” Seals
A dynamic radial seal creates a barrier or interface between surfaces
in relative motion. For radial lip type seals, the interface is where the
seal touches the shaft. Sealing is accomplished by two surfaces making
contact radially, one usually stationary while the other rotates.
A
B
As a shaft rotates in a stationary
housing, a CRW1 dynamic radial
seal both retains lubricant and
excludes contaminants (fig. 2c).
An example of a radial seal is shown in figure 2c. As the shaft rotates
in a stationary housing, a CRW1 seal both retains lubricant and
excludes contaminants. Typical radial seal applications include
gearboxes, drives, motors, pumps and speed reducers.
Axial Mechanical Seals
Axial mechanical seals are face type seals which create an axial
seal interface between matched, radially mounted components. In
operation, one contact face is usually stationary in the housing while
the other moves with the shaft. Sealing pressure is applied in the
axial direction through a spring mechanism. The spring force keeps
the surfaces together.
Axial mechanical seals create an
interface along the shaft plane
between matched components.
Usually, one contact face is stationary
while the other rotates with the shaft
(fig. 2d).
Axial mechanical seals are generally used where pressure and/or
surface speeds exceed the capabilities of radial shaft seals. Typical
applications are water pumps and most types of pumps used in
chemical processing plants or refineries. Figure 2d is a view of
such an installation.
Other types of axial seals are “non-mechanical” ones, such as V-Rings.
Seal Inter face
“Interface” is the point of contact between sealing surfaces (fig. 2e). But
they do not really “contact” at that point, they are separated by a film
of lubricant as thin as 0.00001 in.—a hundred thousandths of an inch.
In metrics, that is 0.25 microns.
The lubricant film prevents rapid wear of the seal lip and/or the shaft
surface. But interface tolerances must be precise to keep the lubricant
from leaking. Uncontrolled conditions of run-out must be prevented.
Any misalignment or eccentricity of interfacing surfaces which exceed
acceptable tolerances must be corrected.
At the “interface” point, a thin film
of lubricant separates sealing surfaces
(fig. 2e).
6
Factors Affecting Seal Selection
2
Every seal application has a unique set of characteristics that must be
analyzed in order to specify the exact style and type of seal (fig. 2f).
Selecting the right seal depends on the basic parameters of the
application, including:
• Shaft speed
• Fluid compatibility
• Primary seal function (retention or exclusion)
• Operating pressure
• Maximum temperature
How to Measure Speed
Surface speed at the point of contact between the seal and the
shaft (fpm: feet per minute, or mpm: meters per minute) is generally a
better indicator of seal performance than revolutions per minute (rpm).
To convert rpm to fpm, use the following formula or refer to the
SKF Handbook of Seals.
.262 x rpm x shaft diameter = fpm (feet per minute)
To convert rpm to mpm, use the following formula or refer to the
SKF Handbook of Seals.
3.142 x .001 x rpm x shaft dia. (mm) = mpm (meters per minute)
or
3.142 x .001 x rpm x shaft dia. (mm) / 60 = ms (meters per second)
Factors such as shaft
speed, operating pressure,
internal and external
temperature, all affect
proper seal selection (fig. 2f).
Pressure
The more pressure applied to a seal, the greater the friction and heat.
That means faster wear and shorter seal life. Most SKF bonded oil seals handle
pressure up to 10 psi (.07 MPa), at speeds from 0 to 1000 fpm (5.08 m/s).
For complete pressure ratings, consult the SKF Handbook of Seals.
Temperature/Fluid Compatibili ty
Another consideration affecting seal selection is temperature and
fluid compatibility. Handbook listings are given in “continuous” ratings—
the relatively constant ambient temperature next to the seal, or the
temperature of the lubricant it retains.
When operating conditions are under O˚F or above 200˚F
(-17 -93˚C), , the range recommended in the Handbook must be
considered in selecting the type of sealing material.
7
BASIC SEAL TYPES (cont.)
As was earlier stated, SKF’s standard nitrite compound provides good
service in most sealing applications from -40˚F to 250˚F (-40˚C to
121˚C). However, silicone, polyacrylate, Longlife or PTFE may be more
suitable for and should be considered for temperatures outside this
range.
For more information on the temperature compatibility and abrasion
resistance of various seal lip materials, turn to Chapter 4.
When a seal’s basic
function is to retain,
face the seal lip toward
lubricant (fig. 2g).
Most applications for shaft seals involve the need to retain or separate
lubricants from some form of external contaminant or abrasion. But
many times it must be determined which is more important, retention
of lubricant or exclusion of foreign matter.
Retention
When the seal’s basic function is to retain lubrication, pressure, or both,
the lip of the seal (generally the spring side) must face toward the
lubricant or the pressure being retained and generally be spring
assisted (fig. 2g).
Exclusion
When the seal’s basic function
is to exclude, face the seal lip
toward contaminants (fig. 2h).
Most bearings fail from the entrance of foreign material and from the
loss or degradation of lubricant. Dirt, abrasives, water and other liquids
can interfere with the film of lubricant required to support the moving
parts of a bearing in a sealed system. Reliable excluders generally
include V-Rings and non-spring loaded seals.
Therefore, it’s vitally important for the seal to keep those materials
from entering the bearing cavity. When the seal’s basic function is to
exclude, the lip of the seal should face toward the contaminants
instead of toward the bearing (fig. 2h). However in this case, only
grease lubrication should be used since oil loss could be excessive.
Retention/Exclusion
For retention/exclusion applications,
a combination of seals in a unitized
assembly can be the best solution
(fig. 2i).
8
Some extreme applications require the seal to perform both the
retention and exclusion functions at the same time. For example, the
seal may need to confine a lubricant while excluding dust or cleaning
solutions. In this case, a special type of protection is necessary either
a combination of seals back-to-back or dual sealing elements within
one unitized assembly (fig. 2i).
Summar y
2
There are many factors involved in selecting seals. To avoid confusion,
the SKF Handbook of Seals contains a “Recommended Operating
Conditions” selection chart to assure a correct seal choice. All of the
selection factors are grouped together along with recommendations
about the type of seal to use in almost every application.
Seal Components
There are five basic seal components (fig. 2j), each performing
a particular function. They include:
• Outer Shell (Case). The outer, cup-shaped, rigid structure
(metal or rubber over a metal case) of the lip seal assembly.
Primarily used for holding the seal in place. The lip is generally
bonded to the outer shell. (A)
• Inner Shell (Case). A rigid cup-shaped component of a seal
assembly, which is placed inside the outer seal case. Reinforces
the outer shell. Can also function as a shield or spring retainer
device. (B)
• Primary Lip (Head Section). The flexible elastomeric component
of a lip seal which contacts the rotating surface. Normally points
toward the most important sealing job, either retaining or
excluding. (C, D)
A
F
B
C
D
E
Each of the seal’s basic
components contribute to its
function (fig. 2j).
• Secondary Lip (Auxiliary Lip). A short, non-spring loaded lip which
is located at the outside seal face of a radial lip seal. Used to
exclude contaminants. Used only in dual lip designs. (E)
• Garter Spring. A coiled wire spring with its ends connected.
It provides a controlled radial load for the lip/shaft interface. (F)
9
CHAPTER 2 REVIEW
To take this test, simply place a card or sheet of paper under the first question. After
you’ve read it (and answered it to yourself) slide the paper down below the next question.
The correct answer to the first problem will appear directly to the right of the new
question. Be sure not to skip any questions.
1. A shaft seal is a barrier designed to retain lubricants and _________________.
❑ a. confine pressure
❑ b. exclude dirt
❑ c. separate fluids
❑ d. all of the above
1. D
2
The _________________ of a seal is a cup-shaped rigid structure that
protects the head of the sealing element.
❑ a. primary lip
❑ b. outer shell (case)
❑ c. inner shell (case)
❑ d. garter spring
2. B
3. Typical radial seal applications include _________________.
❑ a. gearboxes
❑ b. motors
❑ c. pumps
3. D
4. Selecting the right seal depends on application parameters, including
_________________.
❑ a. shaft speed
❑ b. fluid compatibility
❑ c. operating pressure
4. D
5. When the seal’s basic function is to retain, the lip of the seal should
face away from the lubricant or pressure being retained.
❑ True ❑ False
5. F
6. More bearings fail from the entrance of foreign material than
from loss of lubricant.
❑ True ❑ False
6. T
10
7. The function of static seals is to create barriers between relatively
non-moving surfaces.
❑ True ❑ False
2
7. T
8. Axial mechanical seals are generally used where pressure and/or surface
speeds are more than radial shaft seals can handle.
❑ True ❑ False
8. T
9. Seal “interfaces” is the point of contact between sealing surfaces, but do not
actually contact because they are separated by a film of lubricant.
❑ True ❑ False
9. T
10. Revolutions per minute (rpm) is generally a better indication
of seal performance than feet per minute (fpm).
❑ True ❑ False
10. F
11. The more pressure you apply to a seal, the greater the frictional heat
and faster the shaft wear.
❑ True ❑ False
11. T
12. Sealing lips of SKF’s standard nitrile compound are correct for all applications.
❑ True ❑ False
12. F
13. Reliable exclusion seals include V-Rings and non-spring-loaded seals.
❑ True ❑ False
13. T
14. Retention/exclusion applications, sometimes require a combination of
seals in one assembly.
❑ True ❑ False
14. T
15. The sealing lip is generally bonded to the seal’s inner shell.
❑ True ❑ False
15. F
11
CHAPTER 3—
SEAL DESIGN GROUPS
Basic Design Groups
Seals with similar functional abilities are categorized into design
groups. Note that design codes are unique to each manufacturer,
and the ones listed below are codes used by SKF.
HM14
G
FF
Non-Spring Loaded Seals
HM21
TL
These seal designs are typically used for grease retention or dirt
exclusion in slower shaft speed applications.
HD
HMA
The seals illustrated in fig. 3a, HM14 and HM21, are SKF’s standard
designs. Agricultural equipment and quarry conveyor systems are
typical uses. They can also be used as light-duty rod wipers. Other
designs include FF, G, HD, HMA and TL. The heavy-duty TL seal is
designed for severe conditions such as disc harrows. For maximum
dirt exclusion, they should be installed with the lip facing outward.
SKF’s non-spring loaded designs (fig. 3a).
Non-spring loaded seals are not intended for lube oil retention.
Non-spring loaded seals, especially the HM design, are generally
less expensive than spring-loaded versions, and generally cost much
less than the assembled seals they replace. They also provide a good
level of performance when sealing grease.
HDW1
CRWA1
CRW1
CRWHA1
CRWA5
HMS4
SKF’s standard spring-loaded
designs are typically used to retain
oil and/or exclude dirt in higher
shaft speed applications (fig. 3b).
Spring-Loaded Seals
These seal designs are typically used to retain oil and/or exclude
dirt in higher shaft speed applications (fig. 3b). SKF’s standard designs
include: single lip, dual-lips, and single and double shell designs.
The dual-lip design features a non-interference auxiliary lip for added
exclusion protection without the heat build-up associated by traditional
dual-lip designs. Typical applications include gearboxes, speed reducers,
transmissions, motors and drive systems. CRW5 and CRWA5 types
are designed for high pressure applications, up to 90 psi (.62 MPa).
For maximum dirt exclusion, they should be installed with the lip facing
outward. While this works well with grease, be aware of potentially
high levels of oil leakage. The large diameter seal HDW1 type is
designed for severe conditions.
Spring-loaded seals provide longer, more consistent service life
in radial applications than non-spring loaded designs, and better
sealability over a wide range of conditions. They also perform
exceptionally well in applications where there is shaft run-out
and shaft-to-bore misalignment.
12
Case Const ruction
Seal cases are constructed with either metal or rubber outer
diameters. The reasons for these different constructions—their features
and benefits—are as follows:
3
Metal O.D.
Metal O.D. seals feature a metal outer shell or case (fig. 3c). They are
also available with an inner metal shell. The double metal shell provides torsional stiffness and assists in installation, especially where the
assembly of the shaft is against the lip, or for “hammer” assembly
of larger seals.
Dual-lip versions of metal O.D. seals are available in many selected
sizes.
Applications for metal O.D. seals include engines, drive axles,
transmissions, pumps, electric motors and speed reducers. Overall,
the metal-clad CRW seals are recommended over the more basic
HMS seals for most applications.
CRW1
CRW1 features a metal outer
shell or case (fig. 3c).
Metal O.D. seals perform well as economical, general-purpose designs
and provide an exceptionally wide application range.
Rubber O.D.
Rubber O.D. seals feature rubber molded around a steel stamping
(fig. 3d).
They are generally required for split housings and light alloys that are
subject to thermal expansion or gaseous media.
Rubber O.D. seals can withstand reasonable abuse during installation,
and can be inserted in imperfect or rough bores. Their construction
provides limited additional rust resistance. Dual lip versions are
available for many size combinations.
HMS5 features rubber
molded around a steel
stamping (fig 3d).
13
SEAL DESIGN GROUPS (cont.)
Hydrodynamic Seals
One of the most significant developments in sealing technology
occurred in the 1950’s with the introduction of hydrodynamic seals.
Hydrodynamic seals have molded projections added to the seal lip
which enables the seal to pump oil into the oil pump, improving
lubricant retention.
Standard hydrodynamic seal designs
feature helical ribs, parabolic ribs or
triangular pads (fig. 3e).
There are a variety of molded projections used in hydrodynamic
seals. Standard designs have a series of helical ribs, parabolic
triangular pads molded to the lip (fig. 3e). However, these designs
are not without their problems. As dirt builds up against the seal lip,
the lip wears, eliminating the hydrodynamic projections. They can also
become clogged with carbon or dirt. Some hydrodynamic designs are
uni-directional, and can actually pump lubricant out if installed incorrectly.
SKF developed a new type of hydrodynamic seal in the early 1970’s.
Called “Waveseal”, this design features a sealing lip molded with a
sinewave pattern. This traces a wavy path over the surface of the
rotating shaft.
Waveseal
In technical terms, the SKF Waveseal is a smooth lip,
bi-rotational hydrodynamic, molded radial lip seal. More simply, it is a
shaft seal that pumps lubricant back into the sump while sealing out
contaminants no matter which way the shaft is turning.
Steep Angle
Scraper
Low Angle
The Waveseal by SKF
Steep Angle
Scrapes Oil
Inward
• Offers longer, more dependable performance and service life than
conventional trimmed lip seals and other hydrodynamic designs.
Low Angle
Permits Oil
To Slide
Under Lip
Shaft
Rotation
• Has almost universal applications
• Is the first standard line of shaft seals incorporating hydrodynamics
Static
Contact
Path
How Waveseals Work
Dynamic
Contact
Path
Air Side
Oil Side
Oil Particles
The SKF Waveseal touches the shaft
in wide ‘sine’ or wave pattern. Due to
this unique design, contact pressure
and grooving are minimized, heat
generation and friction are reduced.
Lubricant is pumped back to the
bearing while dirt is pushed away
from the lip/shaft interface (fig. 3f).
14
The Waveseal by SKF makes a sweeping contact with the shaft. Its
unique, specially molded lip rides the shaft forming a sinusoidal or
wave pattern around the shaft surface (fig. 3f).
This unique pattern generates less heat, reduces shaft wear and
provides greater lip lubrication than standard lip designs. Its pumping
power is maintained at the same level throughout its service life.
Advantages
+ Traces wavy path over the surface of the shaft.
+ Generates 25-35% less heat at the contact point. This reduces early
seal failure from heat checking, blistering, hardening or lubricant
breakdown.
3
+ Generates 20% less friction torque or drag.
+ Pumps liquid back into the sump while ingesting substantially
fewer contaminants.
+ Bi-rotational hydrodynamic radial lip design outlasts any other
seal of its kind.
+ Performs regardless of lip wear.
Waveseal Designs
Waveseal is SKF’s standard seal design, with over 3,500 part numbers
to fit inch shaft diameters from 0.250” to 12.250”; metric shafts from
12mm to 280mm.
CRW1, CRWH1
Single-lip, spring-loaded Waveseals (fig. 3g). CRW1 is designed without
an inner case. It is recommended for most general purpose applications engines, drive axles, transmissions, pumps, electric motors and
speed reducers. CRWH1 has an inner case for greater strength and
sealing lip protection. It is recommended where shaft assembly is
against the lip.
CRW1
CRWH1
CRW1 is designed without an inner
case. CRWH1 has an inner case for
greater strength and sealing lip
protection (fig. 3g).
CRWA1, CRWHA1
Dual-lip, single element Waveseals feature a no-interference auxiliary
lip that excludes dirt (fig. 3h). CRWA1, designed without an inner case,
provides medium-duty dirt exclusion. CRWHA1, designed with an
inner case, also provides medium dirt exclusion, but for heavier duty
applications. (They also are used when the sealing lip requires
protection during shaft assembly or operation.)
CRWHA1
CRWA1
CRWHA1, with an inner case,
excludes medium dirt in heavier
duty applications. CRWA1
Waveseal has no inner case,
provides medium-duty dirt
exclusion (fig. 3h).
15
CRWA5, CRW5
Waveseals designed without an inner case, CRWA5 has a dual lip
(fig. 3i) and CRW5 has a single lip sealing element. Both are designed
specifically for applications in pressurized seal cavities, up to 90 psi
(.62 MPa).
Large Diameter Metal Clad Seals
CRWA5
CRWA5, with a dual lip, is designed
for applications in pressurized seal
cavities (fig. 3i).
Large diameter seals fit shafts 8” (203.20 mm) in diameter and larger.
They come in two basic designs HDS metal clad and HS non-metal
clad (all rubber) seals.
Metal Clad Seals (Type HDS)
Encased in a heavy-duty steel shell, metal clad seals (type HDS)
are specifically designed to withstand the conditions encountered in
heavy-duty applications. These conditions range from slow speed,
abrasive conditions of a scale breaker to the high-speed operation
of finishing stands. They work exceptionally well in rolling mills,
vertical edgers, logging operations and drag line equipment.
HDS1
HDS1 seal’s Spring-Lock keeps
the spring in position during seal
handling, installation, and removal
(fig. 3j).
HDS2
HDS2 has a Spring-Lock encased
in a flexible Spring-Kover covering
(fig. 3k).
16
HDS type seals are available in three styles HDS1, HDS3 and the
preferred style, HDS2. HDS1 is the basic seal design (Fig. 3j). It has
a single sealing element that features Spring-Lock. The Spring-Lock
270˚ wrap feature keeps the spring in position during handling and
seal installation as well as during seal removal. Spring-Lock is standard
on all three types of metal clad seals.
HDS2 is SKF’s preferred large diameter seal design. It has a single
sealing element and is available with nitrile, Duralip or SKF LongLife
fluoroelastomer lip material. Optional fixed width spacer lugs permit
tandem seal installation, and provide a lubrication gap. HDS2 also
features Spring-Lock encased with a Spring-Kover (fig. 3k).
Spring-Kover is a flexible, resin covering that totally encloses the
garter spring. It is used in sealing applications where dirt or other
contaminants may damage the spring, or where the spring could
be dislodged. The Spring-Kover protects the spring without
affecting its operation.
HDS3’s standard features include adjustable lugs, a Duralip sealing
element for reduced wear and extended service life and a spark-free
inner diameter (I.D.). Other features include Spring-Lock and SpringKover for maximum spring protection (fig. 3l). Spark free I.D. reduces
the chance the seal shell and shaft will come into contact, due to
extreme misalignment or bearing wear. Adjustable lugs allow for
installing two seals in tandem.
HDS seals are available for over 4,600 inch and metric sizes, and new
sizes within catalog guidelines can be created without tool changes or
long lead times.
Siz e
Metal clad seals fit shafts 8” (203.20 mm) to 62” (1574.80 mm)
in diameter.
3
HDS3
HDS3 features a spark-free I.D. which
reduces contact between the seal
shell and shaft surface. (fig. 3l).
Pressure
Pressure tolerance of 10-15 psi (.07 - .10MPa).
Speed
5,000 fpm (25.40 m/s) and greater are possible. The HDS type seal
can handle these speeds in most applications.
Temperature
Handles temperatures ranging from -40˚F to 250˚F (-40˚C to
121˚C) or greater, depending on lip material.
Sealing Element Materials
Nitrile is the standard elastomer base. Duralip, Duratemp and SKF
LongLife fluoroelastomer are also available.
More technical and size information on metal clad large diameter seals
can be found in the SKF Handbook of Seals.
Sealing Combinations
Two metal clad seals, back-to-back or in tandem, provide extra-duty
sealing, cost less and install easier than a double seal. However, in
applications where the bore is not wide enough to hold two seals,
two elements may be combined in one seal assembly.
Dual metal clad types are described below.
HDSA
HDSA has a single, spring-loaded sealing lip combined with
a non-spring loaded auxiliary lip for maximum exclusion (fig. 3m).
There are two designs available. HDSA1 has Spring-Lock; HDSA2
has Spring-Lock and Spring-Kover. In both designs, the auxiliary lip’s
chamfer faces the spring-loaded lip, allowing easier shaft insertion
from the direction of the springloaded lip.
HDSA
HDSA seal is designed with
or without a Spring-Kover
(fig. 3m).
17
HDSB
HDSB
HDSB seal has both a spring-loaded
and non-spring loaded lip (fig. 3n).
HDSB is similar to HDSA in that it also has a non-spring loaded
auxiliary lip combined with a spring-loaded lip (fig. 3n). The chamfer
on the auxiliary lip of the HDSB faces away from the spring-loaded
lip, permitting easier shaft insertion from the back. This eliminates
the need to reverse the direction of the auxiliary lip when the shaft
enters the seal. However, HDSB may be less effective in contaminant
exclusion due to the direction of the auxiliary sealing element.
Two designs are available. HDSB1 and HDSB2 both have
Spring-Lock, while HDSB2 also has Spring-Kover.
HDSC
HDSC
For maximum exclusion of
contaminants, HDCS seal has an
auxiliary lip on the spring side of
the spring-loaded lip (fig. 3o).
HDSC (fig. 3o) is similar to HDSA, but with one exception. The auxiliary
lip is placed on the spring side of the spring-loaded lip and faces the
same direction, providing maximum exclusion of foreign materials.
This style is recommended when excluding foreign materials is more
important than retaining lubricants. When HDSC is installed, both
sealing elements point toward the material being excluded. HDSC
should not be used in oil lubricated systems.
HDSD
HDSD
For separating two fluids, HDSD
has opposing sealing elements in
a single shell (fig. 3p)
Type HDSD has two opposing sealing elements in a single shell
(fig. 3p). That makes this design ideal for separating two fluids in
applications where two individual seals are impractical. Both sealing
lips in HDSD1 have Spring-Lock, while each sealing lip in HDSD2 has
Spring-Lock and Spring-Kover. HDSD can also be used to retain and
exclude.
There must be ample lubrication between the two sealing elements.
Pack the cavity between the lips with grease, or optional drill lube holes
from the O.D. to the I.D. for lubrication for sealing elements can be
provided by SKF.
HDSE
HDSE
Where back-up sealing action
is desired, HDSE’s two sealing
elements serve as two seals in
one (fig. 3q).
18
HDSE has two sealing elements with both lips facing in the same
direction (fig. 3q). This design is recommended in applications where a
back-up seal is desired for retention or exclusion, but there is no room
for two seals. HDSE1 features Spring-Lock on both lips, while HDSE2
features both Spring-Lock and Spring-Kover. If installed to exclude,
grease lubrication should be used for the bearings.
Lubricating the back-up lip is very important, since it could easily run
dry. The primary lip usually stays well lubricated from the fluid being
retained. SKF can provide HDSE with pre-drilled lube holes on the O.D.
EP-2000
The newest member of the HD seal family is the EP-2000
(Extra Performance construction) type HDS7; fig. 3r.
Water and solid contamination ingress is a common cause for
bearing failure. SKF has developed the EP-2000 as a grease seal
with enhanced exclusion capabilities.
The highly engineered EP-2000 features a computer optimized,
springless lip profile designed to retain lubricants and aggressively
pump contamination away from the lip. The increased ability of the EP2000 to exclude contamination makes it an ideal equipment
protector in heavily contaminated environments such as the water
and scale present in rolling mill applications. With this design, the lip
should always face away from the bearings.
HDS7
The springless lip concept of the
EP-2
also reduces radial load.
Radial load can be thought of as the
‘squeeze’ force that the seal exerts on
the shaft. High radial load can lead
to increased seal wear and elevated
underlip temperatures decreasing
seal life (fig. 3r).
3
HDL
The HDL seal (fig. 3s) is a premium metal clad oil seal that is especially
designed to operate in severe conditions including high speeds and
temperatures, high run-out, and high misalignment. The excellent
high-speed performance characteristics of the HDL make it the preferred design in the severe environment encountered in the rolls of
papermaking machines.
Non-Metal Clad Seals (Type HS)
There are two basic types of HS all-rubber seals: solid and split.
All-rubber seals are popular and commonly used where space
limitation and installation difficulties are major considerations. While
metal-clad seals generally provide more positive lubricant retention,
all-rubber seals are an excellent compromise where cost would be high
to tear down and reassemble the unit for the purpose of replacing the
seal. The split type offers a distinct advantage since the equipment
generally doesn’t need to be completely torn down to replace the seal.
Split seals perform best in grease or below-centerline fluid-lubricated
applications on horizontal shafts. They are generally not recommended
for vertical shafts (except for HS8, covered on page 21).
HDL
The HDL features a stainless steel
garter spring that is entrapped by
individual finger springs, also made
of stainless steel, around the entire
circumference of the seal. The
spring combination allows the seal
to compensate for severe conditions
in order to maintain high levels of
sealing performance, operational life,
and equipment reliability (fig. 3s).
19
Cover Plates
All HS seals require a cover plate
for proper fit (fig. 3t).
All HS type seals, split and solid, require the end-user to fabricate and
use a cover plate for proper fit (fig. 3t). The cover plate provides axial
compression and supplements radial press-fit to ensure a leakproof
seal. Refer to Large Diameter Split Seal Installation section for details.
Solid Designs (HS3, HS4, HS5)
The differences between these three designs lie in the shape of the
sealing element and the method of retaining the garter spring.
HS3
HS3
The HS3 all-rubber seal has a spring
held in an open groove, permitting
easy access to the garter spring (fig. 3u).
HS3 is an all-rubber seal with a single spring-loaded element (fig. 3u).
The spring is held in an open groove which permits easy access to the
garter spring. This design is recommended for vertical and horizontal
shafts (Split version: HS9). Limited availability. All new machine
designs, and field replacements, should be made with HS4 or HS5.
HS4
HS4 is an all-rubber seal with a single spring-loaded element (fig. 3v).
The Spring-Lock secures the spring during installation regardless of
the direction of shaft entry. It is recommended for vertical and
horizontal shafts and for use with a cover plate. It is used in steel mills,
work rolls and other applications requiring frequent shaft removal
and installation. (Split versions: HS6).
HS5
HS4
The HS4 all-rubber seal’s spring is
secured by a Spring-Lock (fig. 3v).
HS5 is identical to HS4, except that it also has a Spring-Kover (fig.
3w). HS5 is recommended in applications where materials could affect
the garter spring or when installation can cause the spring to pop
out (Split versions: HS7 and HS8). It can be used for vertical shaft
assemblies in flooded conditions.
Spli t Designs (HS6, HS7, HS8, HS9)
Split seals are recommended in applications where downtime is
critical and shaft disconnection is impractical. The split seal design
offers a distinct advantage over solid seal types. It is placed around
the shaft, the spring connected and then the seal is pushed into the
seal bore. A cover plate provides axial and radial compression
and butts the split ends together.
HS5
HS5 is the same as HS4, but with
a Spring-Kover to provide added
protection (fig. 3w).
20
Split seals perform best in grease applications or on well-lubricated
horizontal applications where the oil is below the shaft centerline.
Split seals generally have poor pressure sealing capability.
HS6
Recommended for general operating requirements, HS6 is
an all-rubber split seal with a single spring-loaded element and a
Spring-Lock. HS6 has a separate loose spring that can be removed
easily so the ends may be connected during installation. A hook-and
eye type spring connector is used with HS6 seals for shafts over 18”.
A threaded type spring connector is used on smaller sized seals.
For proper fit, a cover plate is required.
3
Note: HS7 and HS8 split seals are preferred where separate seal
and spring installation is unnecessary.
HS7
The most easily installed split seal design, HS7 is an all-rubber seal
with a single spring-loaded element (fig. 3x). It has both Spring-Lock
and Spring-Kover. A special guide wire joins the seal together, making
it very easy to install (fig. 3x). After installation, the spring is reconnected
by simply running the control wire into the center of the spring coil
across the split (butt joint). For proper fit, a cover plate is required.
Because this sealing arrangement is not as positive as HS8 (see
below), HS7 is recommended for retaining only grease lubricants on
horizontal shafts at speeds under 1,500 fpm (7.62 m/s).
HS7
HS7 seal is all rubber
with single spring protected by
Spring-Lock and Spring-Kover.
HS7 seal’s guide wire makes
installation easy (fig. 3x).
HS8
HS8 is an all-rubber seal with a single spring-loaded element (fig. 3y).
It features a positive spring connection (hook-and-eye or threaded) in
addition to its Spring-Lock and Spring-Kover. The spring is enclosed
except for a small portion on either side of the split. Unlike other HS
split seals, HS8 is recommended for vertical shafts.
Since HS8 provides the most positive seal of all split type designs, it is
the preferred design in applications for the retention of light lubricants
and water exclusion. It also is recommended for sealing light oils and
heavy greases as well as in applications where there could be extreme
misalignment or run-out. HS8 performs best on horizontal shafts, but
may be used on vertical shafts that are not oil flooded at speeds up to
2,000 fpm (10.16 m/s).
HS8
HS8 features a positively connected
spring protected by a Spring-Lock
and Spring-Kover. It is the most
secure and versatile split seal (fig. 3y).
HS9
HS9 is identical to the HS3 solid seal except that it is a split design.
It is recommended in applications requiring grease retention on
horizontal shafts at speeds up to 1,500 fpm (7.62 m/s). HS9 can seal
lighter lubricants or work at higher speeds only if misalignment or run
out are not excessive. This seal has a narrow cross section and is
designed for smaller shaft size, under 9” (228.6mm).
Limited availability. All new machine designs, and field replacements,
should be made with HS6 or HS8.
21
SBF and HSF
SBF
SBF
HSF
All rubber seals do not score the
bore after repeated installations
and extractions. This prevents
damage to the metal that can
cause bypass leakage (fig. 3z).
The SKF family of all-rubber seals includes metal inserted (SBF)
and fabric reinforced (HSF) products (fig. 3z). The fabric-reinforced
series is available as solid round or with an open joint (split). When
required by customers, they can be used interchangeably with all
rubber HS types and are often found in imported heavy industry
machinery. The inserted SBF type is an alternative to solid HS or
HSF all rubber seals that eliminates the need for a cover plate.
All-rubber seals do not score the bore even after repeated installations
and extractions. This prevents damage to the metal that can cause
bypass leakage. All rubber-seals accept rougher bore finishes, reducing
machining costs. They are especially helpful for split housings. They
resist corrosion and will not seize in the bore even years after assembly.
Multiple Spli t Seat Installation
When split seals are used in multiples, it is necessary to separate the
seals and provide extra lubrication between them. For the best results,
a slotted washer should be fabricated and installed between the seals
(fig. 3aa). SKF does not supply slotted washers.
For best performance, multiple split seals should have staggered
butt joints, for example: one joint at 10 o’clock, the other at 2 o’clock.
A
B
Slotted washer installed between
seals provides room for extra
lubrication when needed (fig. 3aa).
V-Rings
The V-Ring is an all-rubber seal that mounts directly on the shaft
by hand, and is then pushed axially against a counterface, housing,
bearing race or similar surface. Usually made of nitrile or flouroelastomers, other compounds may be obtained on special orders.
Designed with a long flexible lip, it acts like a mechanical face
seal, or a flinger. The V-Ring can be used as the primary seal or
as a back-up seal, to retain lubricants or exclude contaminants. The
V-Ring, which has very high surface speed capabilities, can run without
lubrication. Minimal friction and heat buildup results in extended seal
life. V-Rings running over 1600 FPM (8.13 m/s) may require axial
support and radial retention at even higher velocities.
Its design is based on three components: The body, a conical
self-adjusting lip, and a hinge. The elastic body adheres to the rotating
shaft while the actual sealing occurs at the point of contact between
the conical lip and counterface. The counterface can be the end of a
bearing, washer, suitable steel stamping or even the back of an
oil seal case. The V-Ring’s flexible hinge causes the sealing lip to apply
very light contact pressure against the counterface. Generally, fine shaft
or countersurface preparation is not necessary.
22
Because of its elasticity (the V-Ring stretches up to 2 1/2 times
its molded diameter), the V-Ring can be easily mounted without
disassembling the shaft—even over flanges, pillow blocks and other
assemblies. V-Rings also may be split, rejoined by hot bonding (down
to approximately 18.000”(459.20 mm shaft diameter), or cold-bonded
and used for difficult installations.
3
V-Ring Fi tted Dimension
The fitted dimension of the V-Ring is known as the B1 dimension
(fig. 3bb). This dimension changes as shaft diameters increase. It is
very important when installing a V-Ring. The distance from the back
or “heel” of the seal to the counterface (this is where the sealing lip
contacts the surface axially) must be strictly adhered to. This
dimension is listed as “seal width” in the SKF Handbook of Seals,
V-Ring size listings section. Other key dimensions are also found in
the handbook. There are no requirements for special machining, tight
tolerances or stringent finishes to apply the V-Ring into an existing
application. In most cases it can be retrofitted with little or no changes
to the equipment.
B1
The fitted dimension of
the V-Ring is called “B1”
dimension (fig. 3bb).
Appli c at i o n s
The V-Ring is suited for direct shaft mounting in sealing applications for:
• Conveyor rollers
• Transport equipment
• Rolling mills
• Agricultural machinery
• Paper mills
• Grinding equipment
• Appliances
Styles
V-Rings are available in five styles. Standard material is nitrile;
fluoroelastomer compounds are available in many sizes and special
compounds can be quoted. V-Rings for shafts 8.000” (203.20 mm)
and over can be cut and rejoined by hot or cold bonding. Smaller
nitrile V-Rings can be cold bonded. Note that cold bonding of LongLife
materials is not possible at this time.
VR1
VR1
VR1 is the most common
style V-Ring (fig. 3cc).
Ideal for conveyor rollers and appliances, VR1 is the most common
style (fig. 3cc). It is available in the widest range of sizes from .110”
to over 78.74” (3mm to 2000mm) nitrile and fluoroelastomer lip
materials are available as standard. Other compounds can be quoted.
23
VR2
VR2 is the original V-ring (fig. 3dd).
VR3
A narrow axial cross-section makes
VR3 ideal for certain applications
(fig. 3ee).
VR2
This is the original V-Ring (fig. 3dd). It is designed with a wide body
and tapered heel which holds the seal firmly against the shaft and acts
as a deflector.
VR2 is available in sizes ranging from .177” to 8.270” (4.50mm
to 210mm). It is generally used in contaminated industrial and
agricultural applications.
VR3
With its very narrow axial cross-section, VR3 is excellent for use in
pillow blocks to supplement or replace labyrinth seals or where the
fitted width (B1) is not adequate for a style VR1 (fig. 3ee). VR3 is
available with nitrite and fluoroelastomer lip materials, in sizes that
fit shafts ranging from 4.13” to 79.724” (110mm to 2000mm).
VR4
VR4
VR4 is heavy-duty large diameter
V-Ring (fig. 3ff).
Known as the heavy-duty large diameter V-Ring, VR4 is commonly
used in rolling mills as a dirt/water excluder (fig. 3ff). Sizes range
from 11.811” to over 78.740” (300mm to over 2000mm) shaft
diameter. VR4 is available in nitrile and flouroelastomer.
VR5
VR5
The heavy-duty, large diameter VR5
is ideal for steel mills, ball mills and
papermills (fig. 3gg).
This heavy-duty, large diameter style V-Ring can be easily fitted with
a standard clamping band for axial location in high-speed and large
diameter applications (fig. 3gg). VR5 is ideal for steel mills, ball mills
and paper mills. It is available for shaft diameters from 11.811” to
over 78.740” (300mm to over 2000mm). This design can also be
machined to special widths and lip heights. Available in nitrile and
fluoroelastomer.
VR6
A new version, VR6, is similar except there is no “footer” extension
from the housing (see fig. 3hh). It is available by special quotation. VR4
should be used for most replacement applications. VR6 is a special
order profile mainly used for new machine applications and it will
eventually phase in as a general catalog item.
VR6
VR6 is a new heavy-duty profile
similar to VR5 except it fits a more
compact size (fig. 3hh).
24
Scotseal Oil Bath Seals
SKF Scotseal® PlusXL
Features
The Scotseal ® PlusXL is a rubber unitized, one piece design. The
Scotseal PlusXL consists of four sealing lips; a spring loaded primary
sealing lip with patented Waveseal ® design that is factory pre-lubed,
a radial and axial dirt lip, plus an outer bumper lip that acts as a
preliminary dirt excluder. Scotseal PlusXL requires no special installation
tools and maintains a rubber-to-metal contact between the seal O.D.
and the hub bore surface as well as a rubber-to-metal contact
between the packing I.D. and spindle (see fig. 3ii).
3
Scotseal PlusXL (fig. 3ii).
Benefits
The Scotseal ® PlusXL design with extended life capabilities is the
SKF premium performance seal, offering maximum sealing life under
virtually all driving conditions. The new high-temperature, synthetic
lubricant friendly material of the new Scotseal PlusXL, Hydrogenated
nitrite Butadiene Rubber (HNBR), is an excellent choice for frequent
braking applications. HNBR elastomeric material provides heat
resistance up to 300˚F (149˚C) and broad compatibility with today’s
synthetic lubrication fluids. The unsurpassed exclusion properties allow
the Scotseal PlusXL to perform in very harsh conditions. The new
Scotseal PlusXL with the unique hand-installable design includes
a fat footprint ensuring stability on the shaft. Worn hubs and spindles
are not a problem for the Scotseal PlusXL.
SKF Scotseal® Longlife
Features
SKF Scotseal® Longlife is a unitized, one piece design consisting
of a sealing element (packing) that is assembled between a metal
outer and inner case. The Scotseal LongLife's packing consists of
four sealing lips; a spring-loaded primary sealing lip that is factory
pre-lubed, a radial and axial dirt lip, plus an outer bumper lip that
acts as a preliminary dirt excluder. The Scotseal Longlife is press-fit
into the hub bore using Scotseal Installation Tools. The Scotseal
Longlife maintains a metal-to-metal contact between the seal O.D.
and the hub bore surface as well as a metal-to-metal contact
between the packing I.D. and the spindle (see fig. 3jj).
Scotseal Longlife (fig. 3jj).
Benefits
The Scotseal® Longlife was built upon the success of the original
Scotseal design, which gave SKF engineers a great start in their
development of a new extended life seal. Computer aided design (CAD)
of lip geometry and the addition of an axial dirt excluder lip was
combined with a newly formulated material to produce Scotseal®
Longlife–a premium performance seal with the characteristics
required by many of today’s demanding heavy duty environments.
25
SKF Scotseal® Classic
Features
Scotseal Classic (fig. 3kk).
SKF Scotseal ® Classic is a unitized, one piece design consisting of
a sealing element (packing) that is assembled between a metal outer
and inner case. The packing consists of three sealing lips; a springloaded primary sealing lip that is factory pre-lubed, a dirt exclusion
lip, and an outer bumper lip that acts as a preliminary dirt excluder.
The seal is press-fit into the hub bore using Scotseal Installation Tools.
The Scotseal Classic maintains a metal-to-metal contact between the
seal O.D. and the hub bore surface as well as a metal-to-metal contact
between the packing I.D. and the spindle (see fig. 3kk).
Benefits
The original Self Contained Oil Type Seal, Scotseal® Classic became
the trucking industry standard—and the best value for more than 30
years. With literally trillions of road miles to its credit, Scotseal Classic
has proven to be a solid choice for dependable, long lasting service.
Time and time again, field studies show that when properly installed,
using SKF tools and procedures, Scotseal Classic is a reliable performer
for meeting the sealing requirements between brake maintenance
intervals.
Heav y-Duty Mechanical Seals
SKF heavy-duty, dual face (HDDF) seals are used where positive
lubrication retention and dirt exclusion are both required (fig. 3ll).
Typical applications include mixers, mining equipment, grinders, rollers,
off-road equipment or wherever abrasive contaminants would cause
failure of a general purpose seal.
SKF’s HDDF seal is designed
for applications requiring both
positive lubricant retention and
dirt exclusion (fig. 3ll).
For protection against damage or
contamination, a special retainer
holds the two sealing ring faces
together (fig. 3mm).
26
Features
SKF’s heavy-duty DF seal operates on the principle that two lapped
mating surfaces—a sealing ring and a mating ring—rotate against the
other at right angles to the shaft. This forms an ideal, leakproof seal.
Each one is composed of four components: two identical, high alloy,
corrosion resistant steel sealing rings and two similar, opposed
Belleville washers of compounded elastomers, one with a patented
retainer lip. The seal fits easily into conventional, straight bore housings, with neither special machining or polishing of the bore required.
Benefits
Extensive testing under rigorous conditions proves that the heavy-duty
DF seal performs dependably at least ten times longer than soft face
designs, and three times longer than other metal face designs.
The one-piece heavy-duty DF seal installs simply by hand. No special
tools or jigs are required. A small retaining lip on the O.D. edge of one
of the washers holds and centers the entire seal in the bore while the
assembler installs the companion bore or flange.
Axial Clamp Type Seal
Chock
Primary
Seal
Axial Clamp Seals
Axial clamp seals (fig. 3nn) are recommended especially for large
diameter applications where additional protection from heavy amounts
of contamination is required for the primary seal. Examples include
steel and paper mill rolling equipment, logging operations, and rock
and ore crushing applications. Clamp seals are available in 3 design
variations and are intended for stationary mounting, usually on
horizontal shoulders though they can also be mounted vertically. The
clamp seal must be fitted against a positive stop. Assembly is usually
easily done by wrapping around the shoulder diameter and tightening
the stainless steel screw clamp. The seal may have no gap at the
ends (butt joint) or an optional drain gap.
3
Roll
Fillet Ring
A stainless steel screw type
clamp secures and locks the axial
clamp seal in place (fig. 3nn).
Stator
Bearing
Flouroelastomer
O-rings
Defender bearing isolator
A new sealing concept known as the bearing isolator relies on very
small internal clearances and dynamic non-contacting technology.
SKF’s Defender isolator is an assembled, two-piece labyrinth or gap
seal utilizing a stator element pressed into the housing bore and a
rotor fixed to the shaft. Fluid or particle contamination trying to enter
the machine system is limited by the small labyrinth gap. Any that does
get into the labyrinth is collected and expelled out a port at the bottom
of the seal. Grease or oil lubricants can be contained so long as they
do not flood the seal stator, however the Defender (fig. 3oo) itself can
run dry indefinitely. Besides highly effective contaminant protection,
bearing isolators offer long service life with virtually no torque drag,
friction or power loss. Defender isolators are stocked for specific
equipment applications or can be produced to the necessary dimensions.
Non-Standard Seal Configurations
SKF seals include a variety of non-standard designs for specific
applications. Fig. 3pp shows sectional views of their configurations.
Engineered for special sealing applications by SKF, they are examples
of the company’s ability to respond to end-users’ unique requirements.
The designs shown are not all available in a complete range of sizes
and/or materials. However, quantities of certain sizes/materials are
inventoried. Whatever application, SKF offers consulting services to help
end-users find stock or custom solutions to their shaft sealing problems.
Shaft
Rotor
Oil Level
Ejection Port
Housing
Defender bearing isolators are
special unitized, two piece seals
that are easily installed into
housing bores (fig. 3oo).
CRS1
FF1
W1
CRSA9
HMA3
X1
D7
HMS4N
X4
HMSA11
X14
Sectional views of SKF’s non-standard
seal configurations. (fig. 3pp).
27
“OLD” DESIGN
“ N E W DESIGN”
Older “clamp-type” seal (left) has
been replaced by newer hydrodynamic
Waveseal (right) (fig. 3qq).
O l d vs. New Se a l D e s i g n s
Following the “original” leather strap seals, the first engineered
designs were known as “assembled” or “clamp-type” seals. They were
assembled by laying two sealing elements and three metal spacer rings
into an outer shell and clamping these components together. They
were wide and sturdy in appearance, and tended to apply high lip
pressure to the shaft, creating shaft wear. A garter spring was placed
against the primary or retention element. The sealing lips were usually
trimmed to size, using a knife.
In today’s designs, the sealing element is molded to size, and
permanently bonded to a metal case (fig 3qq). In modern spring
loaded molded seals, a garter spring is snapped into a mold-formed
groove in the sealing member. Today’s seals are narrower, lighter
and less sturdy in appearance, but their designs give them uniform
compressive sealing force. Only a thin band of lip material rubs against
the shaft so they can operate at higher speeds with less friction.
PTFE seals
General purpose design for lubricated
media and moderate pressure and
surface speeds (fig. 3rr).
Pressure design for service to 5
psi (35 bar). Variations for vacuum
and high shaft speeds (fig. 3ss).
28
SKF PTFE seals (fig. 3rr and fig. 3ss) are assembled or machined,
made-to-order radial shaft seals based on PTFE (Teflon® or
polytetrafluoroethylene). This thermoplastic material has properties
that exceed the capabilities of rubber compounds. PTFE seals can
accept high surface speeds, pressure and dry running conditions and
have high wear resistance and service life. Their temperature range
is very wide and they resist attack by nearly all acids, solvents and
chemical agents. They can be made for variety of inch or metric sizes
from small to large diameter, often without any tooling charge. PTFE
seals generally require a high quality shaft finish and hardness, and
are engineered to meet specific application conditions.
Chapter 3 Review
The correct answer to the first problem will appear directly to the right of the new question.
Be sure not to skip any questions.
3
I . Heavy-duty mechanical seals (HDDF) _________________.
❑ a. retain lubricants
❑ b. exclude contaminants
❑ c. can be used under severe service conditions
1. D
2. The _________________is a smooth lip, bi-rotational hydrodynamic radial lip seal that
pumps lubricant back into the sump while sealing out contaminants.
❑ a. V-Ring
❑ b. metal clad seal
❑ c. Waveseal
❑ d. none of the above
2. C
3. An advantage of the Waveseal is it _________________.
❑ a. generates 20% less frictional torque or drag, which reduces shaft scoring
❑ b. pumps liquid back into the sump while drawing in less contaminants
❑ c. generates 25%-35% less heat at contact, which reduces early seal failure
3. D
4. HS all-rubber _________________ may be placed around the shaft, the spring
connected and the assembly pushed into the seal bore.
❑ a. split seals
❑ b. solid seals
❑ c. both of the above
❑ d. neither of the above
4. A
5. When split seals are used in multiples, a_________________is often used to separate
the seals and provide extra lubrication between them.
❑ a. horizontal shaft
❑ b. slotted washer
❑ c. control wire
❑ d. butt joint
5. B
6. _________________ are dual face mechanical seals used where both positive
lubrication and dirt exclusion are required.
❑ a. Waveseals
❑ b. V-Rings
❑ c. HDDF seals
❑ d. Retention seals
6. C
29
CHAPTER 3 REVIEW (cont.)
7. The V-Ring is an all-rubber seal that _________________.
❑ a. mounts directly on the shaft by hand
❑ b. is sealed axially against a counterface, housing bearing race or similar surface
❑ c. acts like a mechanical face seal, or flinger
7. D
8. Heavy-duty mechanical seals (HDDF) _________________.
8. D
9. _________________ are recommended for large diameter applications where there is a
need for two seals but room for one, as in steel and paper mills or logging operations.
❑ a. Heavy-duty seals
❑ b. Axial clamp seals
❑ c. V-Rings
❑ d. None of the above
9. B
10. HDS metal clad and HS non-metal clad (all-rubber) seals are the two basic types of
large diameter seals.
❑ True ❑ False
10. T
11. Cover plates, required by all HS type seals, provide axial compression and supplement
radial press-fit to ensure leakproof seals.
❑ True ❑ False
11. T
12. Pressure Waveseals (CRW5 and CRWA5) perform better than conventional
lip seal designs in pressurized environments, and can be used to replace some
mechanical seals.
❑ True ❑ False
12. T
13. Type HDSD has two opposing elements in a single shell, making it ideal
for separating two fluids in applications where two seals are impractical.
❑ True ❑ False
13. T
14. PTFE seals can run for long periods of time without lubrication and resist attack by
many acids and solvents.
❑ True ❑ False
14. F
15. Metal clad seals (Type HDS) are incapable of handling high speeds.
❑ True ❑ False
15. F
30
16. Two metal clad seals (Type HDS), back-to-back or in tandem, provide extra-duty
sealing, cost less and install easier than a double seal.
❑ True ❑ False
16. T
17. SKF heavy-duty mechanical seals (HDDF) are not recommended when abrasives or
contamination could cause premature failure of general purpose seals.
❑ True ❑ False
17. F
3
18. Axial clamp seats are difficult to use and require special tools for installation.
❑ True ❑ False
18. F
19. The heavy-duty DF seal has a special retainer to hold the two sealing ring faces
together for protection against damage or contamination.
❑ True ❑ False
19. T
20. The V-Ring’s elastic body adheres to the rotating shaft while the actual
sealing occurs at the point of contact between the lip and counterface.
❑ True ❑ False
20. T
21. An axial clamp seal assembles securely and locks in place with a stainless
steel screw type clamp.
❑ True ❑ False
21. T
22. The heavy-duty DF seal’s seating ring and mating ring rotate against each
other at right angles to the shaft to form a leakproof seal.
❑ True ❑ False
22. T
23. Scotseal oil bath seals have three seating lips: one primary lip to keep oil in,
two secondary lips to keep dirt out.
❑ True ❑ False
23. T
24. Scotseal Plus oil bath seals can be installed by hand, using no more than
common shop tools if any at all.
❑ True ❑ False
24. T
25. Defender bearing isolators require no lubrication but provide highly effective
protection against fluid or particle contamination.
❑ True ❑ False
25. T
31
Chapter 4—
Seal Applications
Seal Selection by Application
When selecting a seal for a specific application, it is important to know
what the seal is supposed to do and what operating conditions are
present. Common types of applications and seal designs recommended
for them are covered below.
Seals for Contaminant Exclusion
In steel mill or work roll applications, an abundance of contaminants—
scale, water spray, abrasive particles—are usually present. The seal’s
primary function is to exclude contaminants and prevent them from
entering the bearing cavity.
V-Ring excludes contaminants,
prevents them from entering
bearing cavity (fig. 4a).
A back-up excluder seal, such as a V-Ring, is recommended (fig 4a).
The V-Ring can function as the primary seal or, in applications where
there is excessive contamination, it can provide protection for the
primary sealing element, increasing its life and reliability.
The V-Ring is designed to exclude dust, mud, water and most
contaminants, and can handle pressures up to 10 psi/.07 MPa (static)
or 3-5 psi/.02-.03MPa (dynamic). An all-rubber design, it stretches (up
to 2-1/2 times its diameter) over the shaft, easing installation.
As the seal rotates with the shaft, centrifugal force provides a “flinger”
effect, keeping out dust, mud, water and most contaminants. Exclusion
seals can be installed axially against any suitable counterface (bearing,
other seal, pillow block, bearing assembly or other housing). They
generally do not require lube for normal operating conditions.
Seals for Grease Retention
Grease lubricated applications, such as electric motors or small trailer
wheels, are generally easier to seal than oil lubricated applications.
When cost is also a factor, a non-spring loaded seal such as an HM
design, is usually the most cost-effective design for grease retention.
(fig. 4b).
Non-spring-loaded HM seal is a
cost-effective design for grease
retention. Note that the lip faces the
lube in this application (fig. 4b).
The HM seal design retains grease at shaft speeds up to 2000 fpm,
(10.16 m/s) and handles pressure up to 3 psi/.02 MPa. It should be
installed with the lip facing the grease, except in applications where
grease purge is desired. In “purge”-type applications, the lip should
face away from the grease lube.
In grease retention applications where contaminants are present,
a V-Ring can also be installed as a back-up excluder.
32
Seals for Oil Retention
Input-output shafts, gearboxes and driveshafts are oil-lubricated
applications. These and other oil retention applications require
spring-loaded seals, either with or without inner shells (fig. 4c).
CRW and CRWA are spring-loaded Waveseals recommended for oil
retention. They should be installed with the lip facing the lubricant.
They are capable of handling shaft speeds up to 3600 FPM (18.29
m/s). While they are designed with nitrile, silicon or LongLife
fluoroelastomer lip materials, the material selected must be
compatible with the lube being used.
Oil retention applications
require spring-loaded seals,
either with or without inner
shells (fig. 4c).
4
Seals for Exclusion/Retention
Some applications require positive oil retention and absolute dirt
exclusion. The best way to solve this problem is with two seals. One
faces the bearing to retain the lubricant. The other faces out to exclude
contamination. A variety of combinations can be used depending on
the space available and the operating conditions.
For very severe dirt, water and mud conditions, SKF has designed
the HDDF series (fig. 4d). Classified as “heavy-duty mechanical” seals,
their typical applications are track rollers and final drives for mining
equipment, earth moving vehicles, mixer and rock crushers.
SKF’s HDDF seal is designed to
provide both positive oil retention
and absolute dirt exclusion (fig. 4d).
The HDDF seal has a dual face construction which retains lube
while excluding water, dirt and abrasive materials. The HDDF resists
abrasives that cause radial type seals to fail. Other seal recommendations
include the G, HD, and HM series seals. These are for light to moderate
dirt exclusion applications at slow shaft speeds.
Recommendations for severe dirt exclusion applications include the
A, B, TL and XTL, which are heavy-duty designs with multiple lips.
Seals to Separate Two Liquids
Sometimes, a shaft runs through two liquids which must be kept
separate. The previous seal design used in this application has two
spring-loaded elements and one seal case. The D7 design has the two
sealing lips point in opposite directions and both are spring-loaded.
There is room between the sealing lips for a grease pack when one is
needed. If necessary, holes can often be drilled from the outer to the
inner diameter to align with existing lubrication grooves. Typical
applications include separating different lubricants in gearboxes,
transmissions and transfer cases.
33
Seal Applications (cont.)
An alternative, more effective solution is to use two seals of the same
design (CRW1 or CRWH1) installed back-to-back. The sealing lips must
be pointed toward the liquid which they are intended to retain. One lip
should face the lube, while the other faces the fluid (fig. 4e).
An effective solution to separating
two liquids is to install two seals of
same design back to back (fig. 4e).
To retain a fluid, a spring-loaded seal should be used. If one side will
be occasionally called upon to run in a dry atmosphere, a compatible
grease pack should be used in the cavity between the two seals to
insure sufficient lubrication at all times.
Seals Used in Combination
To satisfy the needs of particularly difficult applications (such as
multiple requirements in one location) or extreme operating conditions,
seals can be used in combination. Such applications might be rolling
mills and power take-off assemblies, where lube retention and
contaminant exclusion are equally critical.
Sometimes seals are used in
combination to satisfy application
requirements. Here, a V-ring
performs an exclusion function
(fig. 4f).
There are several combinations to choose from, depending on specific
application needs. One solution would be to combine opposed CRW or
HDS seals to retain lube and exclude fine contaminants. Another might
be to use a V-Ring to exclude contaminants and protect radial lip seals
for longer life (fig. 4f).
HDS seals used with V-Rings are usually the correct solution
for applications such as roll necks in milling operations.
Factors Determining Seal Material Selection
A variety of factors are used to
determine selection of proper seal
material (fig. 4g).
Choosing the correct seal for an application requires satisfying a
number of operating conditions (fig. 4g). Among these are the
application’s temperature range, lubricant compatibility, chemical
compatibility, shaft speed(s), shaft surface finish, pressure (internal
or external), contaminants to be excluded, housing material/condition,
and abrasion.
Other factors which should be considered are run-out, shaft-to-bore
misalignment, installation/handling, operating torque and, of course,
cost.
Sealing Element (Lip) Materials
Seals are available with a wide variety of sealing element materials.
Selection should be based on sealing application, compatibility with
lubricants and fluids being retained, operation temperatures and
other operating conditions.
Detailed ratings and recommendations for each material can be
found in the first few pages of the SKF Handbook of Seals.
34
Synthetics
The most popular and versatile sealing element (lip) materials in
use today are synthetics. These include thermoset elastometers such
as nitriles (standard, carboxylated and hydrogenated), polyacrylates,
silicones and fluorelastomers plus thermoplastics such as Teflon™*.
Each material has its own advantages and disadvantages.
Thermoset Elastomers
4
Thermoset elastomers are defined as materials which are
non-reversibly cross-linked through the vulcanization process.
Vulcanization uses heat and catalysts to create strong molecular
bonds linking polymer chains. They compose the largest group of
synthetic compounds. These include nitriles, polyacrylates, silicones and
LongLife elastomers (fig. 4h).
N i t r i le
Nitrile is the most popular material for the majority of sealing
applications today. It is a co-polymer of two basic synthetic compounds
Butadiere and acrylonitrile polymers. Different properties are obtained
by changing the percentage of each polymer used in the mixture
(or copolymer).
Nitrile has generally replaced leather as a sealing lip material.
Operating Range
Seals with nitrile sealing lips are effective in temperatures
ranging from –40°F to 250°F (-40°C to 121°C).
Advantages
+ Good oil compatibility
+ Good abrasion resistance
+ Good low temperature and swell characteristics
+ Good manufacturing qualities
+ Relatively low in cost
D i s a d va n t a g e s
Thermoset elastomers include
nitriles, polyacrylates, silicones
and LongLife elastomers (fig. 4h)
- Not resistant to EP lubes or synthetic oils (phosphate ester, skydrol)
- Not recommended for temperatures over 250°F (121°C)
- Vulnerable to ozone, ultraviolet light conditions
*Teflon is a registered trademark of E.I. DuPont.
35
I d e n t i f i c at i o n
Varies from gray-black to shiny jet black
Subst i tute Materials
Polyacrylate, Duralip, Duratemp or LongLife and LongLife TFE
elastomers.
DURATEMP
A special nitrile compound based on hydrogenated nitrile (HNBR)
Duratemp offers improved tensile strength and resistance to heat,
abrasion, hardening in hot oil, ozone and weathering effects. It is
mainly used in large diameter seals in heavy-duty applications; other
sizes available by quotation.
Operating Range
Hydrogenated nitrile seals can be used from –40°F
to 300°F (-40°C to 149°C).
Advantages
+ Tensile strength typically 50% higher than standard nitrite
+ Ozone and UV resistance considerably improved
+ Heat resistance increased 20% with less reduction in hardness
and elongation, especially in hot oil with additives
+ Better abrasion resistance (equal to Duralip)
L i m i tat i o n s
- Decreased elasticity at cold temperatures
- Lower compression set resistance at cold temperatures
(but better than Viton)
- Should not be considered a universal replacement for Viton
especially considering attack by aerated lubricants and high
temperature physical properties such as compression set
- In some cases, aerated oils can be a problem for HNBR
Visually the same as standard nitrile
Polyacrylate, PTFE and LongLife elastomers (depending on the
operating conditions)
36
DURALIP
Duralip is SKF’s special nitrile compound blended for extreme abrasion
resistance. It is recommended where scale, sand, grit, dirt or other
highly abrasive materials are present. Not usually a stocked compound,
it most often is used for large diameter HDS and HS seals. It can be
quoted for most CRW type seals.
Advantages
+ Extreme abrasion resistance
+ See nitrile
4
- See nitrile
Operating Range
See nitrile
See nitrile
POLYACRYL ATES
Polyacrylates are elastomers which will function at higher operating
temperatures than nitriles, as well as with extreme pressure (EP)
lubricants. They have limited availability from stock.
Advantages
+ Good compatibility with most oils, including EP additive
+ High resistance to oxidation and ozone
+ Tolerates higher operating temperatures than nitrile
- Low compatibility with some industrial fluids
- Poor compression-set characteristics
- Should not be used with water
- Poor performance in cold conditions
Operating Range
Seals with polyacrylate lips are effective in temperatures ranging
from –40°F to 300°F (-40°C to 149°C).
Generally black; slight gloss when rubbed. May have sharp odor.
37
Nitrile, Duratemp or LongLife and PTFE fluorocarbon lip
materials.
SILICONE
Silicone’s high lubricant absorbency minimizes friction and wear. It can
be used in a wide range of temperatures. Silicone polymers generally
are made only in bonded designs. Limited availability from stock; also
available by quotation.
Advantages
+ High lubricant absorbency, minimizing friction
+ Very flexible
+ Wide temperature range
- Poor compatibility with oils that have become oxidized,
or with EP lube additives
- Tendency to tear and cut during installation
- Poor abrasion resistance
- Tends to wear the shaft
- Relatively high cost
- Attacked by acids, alkalai, hot water and steam
Operating Range
Silicone seals can withstand a very wide temperature range,
from –100°F to 325°F (-73°C to 163°C).
Generally red or orange but sometimes gray or blue. Silicone seals
feel softer and are more flexible than other materials.
Duratemp, Polyacrylate, LongLife, PTFE and fluoroelastomer lip
materials. Always check the operating conditions.
SKF LongLife
SKF’s LongLife material
extends seal service life under
wide temperature ranges (fig. 4i).
38
SKF’s LongLife fluoroelastomer is a premium synthetic lip formulation
that provides extended service life under wide temperature ranges
(fig. 4i). It also resists degradation caused by the newer chemically
aggressive lubricants. It is compatible with an exceptionally broad
range of media, including most oil additives and synthetic oils.
Advantages
+ Extended service life.
+ Wide temperature ranges.
+ Resistance to attack by lubricants and chemicals that destroy nitriles,
polyacrylates, silicones and other synthetics.
+ Compatibility with rubber solvents (benzene, toluene, carbon
tetrachloride).
4
+ Compatible with wide range of mineral and synthetic lubricants.
+ Low swell characteristics.
+ Excellent abrasion resistance.
+ Superior heat performance and weathering.
- Higher initial cost.
- Can be attacked by some special purpose lubricants, and
fire-resistant fluids.
- Not recommended for applications involving low molecular
weight esthers, ethers, ketones, amines and acids.
- Not the best for cold temperature applications
Operating Range
LongLife fluoroelastomers maintain thermal stability at temperatures
from –40°F to over 400°F (-40°C to over 200°C).
I d e n t i f i c ation
LongLife materials are brown or black.
T h e r m o p la st i c s ( PTFE)
PTFE (i.e. Teflon ®) is the most widely used fluoropolymer
thermoplastic. These materials are not cross-linked like most rubber
materials. Instead they are formed by heat and pressure (sintering)
into dense blocks comprised of long carbon and fluorine chains.
Teflon seals perform well at high
surface speeds (fig. 4j).
Teflon seals offer a wide operating temperature range, accommodate
high surface speeds and provide superior dry-running characteristics
(fig. 4j). They feel like plastic, having a waxy texture. These seals are
usually machined or assembled designs.
Advantages
+ Resists nearly all acids, acid-based fluids and solvents
+ Handles wide temperature range
+ Superior dry-running characteristics
+ Extreme wear resistance; longer seal life
39
+ Handles high surface speeds
+ Some blends are food grade compatible
+ Can accept high pressure
+ Service life capability can exceed rubber compounds
- Higher initial cost
- Normally non-stock
- Mechanical properties must be engineered in (Virgin PTFE
has low mechanical strength)
- Extra care is required during assembly
- Difficult to install
- Generally requires higher shaft hardness
Operating Ranges
Thermoplastic PTFE seals handle a wide temperature range, from
–400°F to 500°F (240°C to 260°C).
I d e n t i f i c ation
Red, white, gray, blue, green or brown.
LEATHER SEALS
Once the most popular seal
material, leather is now being
replaced by less expensive
synthetic materials (fig. 4k).
Before synthetic materials were developed, leather was the sealing
element commonly found in most early seals. Leather is tough, resists
abrasion and works well even today in many dirt exclusion applications.
However, it is expensive and can usually be replaced with another lip
material (fig. 4k). SKF stocks very few leather seals.
Advantages
+ Good tensile strength and abrasion resistance
+ Performs well with minimal lubrication
+ Tends to smooth rough shaft surfaces
+ Compatible with most lubes and solvents
+ Good dry running performance
+ Good in very cold temperature operation
+ Tough
40
- Poor compatibility with water
- Non-homogeneous matrix makes
consistent high quality difficult to maintain.
- Expensive
- Vulnerable to heat above 200˚F
- Designs tend to have high torque
- Limited Availability
- Costly
4
Operating Range
Leather can handle temperatures ranging from –100°F to 200°F
(-73°C to 93°C).
It is difficult to determine from the appearance of a used seal whether
the sealing element is leather or rubber. Scratch the sealing surface.
If that makes the surface much lighter (brown or beige) and fibrous,
rather than black and smooth, the material is probably leather.
Subst i tute Lip Material
Nitrile, polyacrylate or fluoroelastomer
FELT
Felt is another non-synthetic material which has long been used as a
sealing material. Made of wool and sometimes laminated with synthetic
rubber washers, felt is generally limited to dirt exclusion. It can be used
to retain heavy lubricants under some conditions.
Advantages
+ Excludes dust and dirt well
+ Retains grease efficiently
- Cannot confine oil
- May trap metal and/or dirt particles, causing shaft wear
- Absorbs water which may cause shaft rusting
- Few stock sizes
Operating Range
- Felt is used in temperatures ranging from –65°F to 200°F
Subst i tute Lip Materials
Nitrile, polyacrylate or fluoroelastomer
41
°C °F
Material Capabilities—Temperature Resistance
PTFE
260° 500°
400°
Viton
200°
Duratemp
Polyacrylate
300°
In performing their sealing function, seal lip materials work best within
the following temperature ranges. (Also see fig. 4l).
Duralip
100° 200°
F˚
C˚
-400˚ to 500˚
-40˚ to 400˚
-240˚ to 260˚
-40˚ to 204˚
-100˚ to
-40˚ to
-40˚ to
-40˚ to
-100˚ to
-40˚ to
-73˚
-40
-40
-40
-73˚
-40˚
100°
0° 32°
0°
Nitrile
-100°
Silicone
Leather
-100°
-240° -400°
Lip materials’ maximum operating
temperatures fall within these
ranges (fig. 4l).
Polytetrafluoroethylene
( P TFE)
Fluoroelastomer
(LongLife)
Silicone
Polyacrylate
Duralip
Nitrile
Leather
Duratemp
325˚
300˚
250˚
250˚
200˚
300˚
to
to
to
to
to
to
163˚
149˚
121˚
121˚
93˚
149˚
Low temperatures can be as much of a problem for a seal as high
temperatures. At low temperatures the sealing material gets stiff
and rigid. That causes several problems. The sealing lip has trouble
following the eccentricity of a shaft that’s not perfectly true. That causes
it to leak every time the shaft rotates “off center” and pulls away from
the seal. If it gets stiff enough, the material becomes brittle and breaks
up with the movement of the shaft. Another problem can appear when
the lip material starts to shrink up at low temperatures.
At high temperatures, some elastomers will continue to cure again
and lose their pliability. If the temperature gets high enough to burn the
lip material, it often becomes hard and brittle. It can crack and break up.
In such cases, it not only loses its sealing effectiveness, it can also
damage the bearing and the shaft it was designed to protect.
Consequently, both upper and lower operating temperature limits
should be considered when choosing a lip material. See fig. 4l for
operating temperature ranges of a variety of lip materials.
42
Material Capabilities—A brasion Resistance
For example, nitrile is a compound of synthetic rubber which is
formulated to optimize pliability and hardness so it covers most
applications. However, other materials are available which offer better
resistance to abrasive contaminants. They’re harder, denser materials,
and dust particles are less likely to become imbedded in them. SKF’s
Duralip compound was developed especially for large-diameter seals
where abrasion resistance is critical. See fig. 4m for relative abrasion
resistance of several lip materials.
8.00
7
7
6
6.00
5
4.00
2
2.00
1
E
fe
Li
PT
F
te
m
p
ra
Lo
ng
Du
Du
ra
l
r
ip
ile
he
at
on
Ni
tr
Le
y
Si
lic
AC
M
e
0.00
Po
l
Fine dust particles and other contaminants can become imbedded
in the surface of a soft lip material and turn it into an abrasive. It
scores the shaft causing deep grooves which render the seal useless
and the shaft in need of repair.
9
Relative Abrasion Resistance
Usually, it’s desirable for a lip material to be soft and pliable. This allows
it to follow the eccentricity of a shaft and form a better seal. But in
extremely dirty environments, a soft material can become a liability.
10
10.00
4
On a scale of 1 to 1 , abrasionresistance capabilities of sealing lip
materials are compared in the chart
above (fig. 4m).
Lip materials offering the best resistance to abrasion are PTFE and
LongLife by SKF. On a scale of 1 to 10, PTFE is a “10.” On the same
scale and not far behind is fluoroelastomer-based LongLife with a
“9.” The abrasion resistance provided by both of these materials is
exceptional, outperforming hydrogenated nitrile’s very good “7.”
43
Chapter 4 Review
1 . Simultaneous exclusion and retention is best performed with _________________ .
❑ a. a combination of two seals back to back
❑ b. single lip design seals
❑ c. a combination of two seals front to back
❑ d. V-Ring seals
1. A
2. _________________ is the most popular material for the majority
of sealing applications today.
❑ a. Leather
❑ b. Felt
❑ c. Nitrile
❑ d. Silicone
2. C
3. Polyacrylates _________________ .
❑ a. are compatible with high operating temperatures
❑ b. offer high resistance to oxidation and ozone
❑ c. may be used with water
❑ d. both a. and b.
3. D
4. Before the invention of nitriles, _________________ was the most common
sealing element.
❑ a. rubber
❑ b. felt
❑ c. leather
❑ d. metal
4. C
5. Popular sealing lip synthetics in use today include _________________ .
❑ a. nitriles
❑ b. fluoroelastomers
❑ c. fluoropolymer (PTFE)
5. D
6. Advantages of polyacrylates include _________________ .
❑ a. good compatibility with most oils
❑ b. high resistance of oxidation and ozone
❑ c. better compatibility with high temperatures than nitrile
6. D
44
7. Advantages of silicone include _________________ .
❑ a. good compatibility with oxidized oils
❑ b. high lubricant absorbency
❑ c. excellent abrasion resistance
❑ d. low cost
7. B
8. Leather is an expensive sealing material that has a good compatibility with water.
❑ True ❑ False
8. F
4
9. V-Rings must be lubricated for all operating conditions.
❑ True ❑ False
9. F
10. For very severe conditions, SKF’s HDDF seals resist abrasives that cause other
seals to fail.
❑ True ❑ False
10. T
11. HDS seals used in combination with o-rings are usually the right answer
for applications such as roll necks in milling operations.
❑ True ❑ False
11. F
12. All of the synthetic materials have the same operating characteristics.
❑ True ❑ False
12. F
13. Nitrile’s disadvantages include poor abrasion resistance.
❑ True ❑ False
13. F
14. Some blends of fluoropolymer seals are food grade compatible.
❑ True ❑ False
14. T
15. Applications for SKF’s LongLife fluoroelastomer lip materials are limited
to standard lubricants
❑ True ❑ False
15. F
16. PTFE can often be used where temperatures and pressure would ruin rubber seals.
❑ True ❑ False
16.T
45
Chapter 5—Seal Selection
The first consideration in selecting a seal is to know:
• Is it a seal for a new application, or
• Is it a replacement seal for an existing application?
Selecting seals for new applications is covered in Chapter 4: Seal
Applications. It would seem that selecting a seal for an existing
application would be an easier chore. Even so, there are
considerations such as:
• Is an exact replacement seal desired, or
• Should an alternative seal be selected which would be a “better”
choice for that particular application?
How to Select a Replacement Seal
If the old seal was manufactured by SKF, you should have no trouble
finding an appropriate identification number and selecting the proper
replacement. SKF seals are identified by:
• SKF stock number
• SKF industrial part number
• SKF drawing number
• OEM part number
This number will tell you exactly which replacement seal is right for
the job. If the part number on the old seal is legible, refer to the SKF
Master Interchange for a replacement.
If you can’t find an identification number, match the old seal’s size
with listings in the SKF Handbook of Seals. If there is no seal listed
with the exact same width, select a narrower one.
Seal Size
W
O.D.
Shaft
Diameter
Seal size is determined by seal
bore, seal width, seal .D. and
shaft diameter (fig. 5a).
46
Seal size (fig. 5a) is determined by:
• Seal bore the diameter of the hole in the housing into
which the seal is fitted.
• Seal Outer Diameter (O.D.)—the press-fit diameter. It’s usually in
the range .004” to .008” (.10mm to .20mm) larger than the bore
for metal O.D.’s. It’s usually .006” to .022” (.15mm to .55mm) for
rubber O.D.’s.
• Seal Width (W)—the total width of the seal including both
the inner and outer shell.
• Shaft Diameter (S.D.)—the outside diameter of the shaft
at the location where the seal is mounted.
Proper Seal Measurement
Two of a seal’s measurements are its outer diameter (O.D.) and its
inner diameter (I.D.). To determine these, follow these procedures:
• To measure the O.D. of a seal, take three measurements
equally spaced around the outside of the seal. The average
of the three is the seal’s O.D. (fig. 5b).
• A metal 0.D. seal is generally 0.005” to 0.008” (0.13mm
to 0.20mm) larger than the bore, for press fit.
• A rubber O.D. seal is generally 0.008” to 0.026” (0.203mm
to 0.508mm) larger than the bore, for proper compression
and interference fit.
5
• The inner diameter is more difficult to measure. Take about
five I.D. readings, average them.
• Allow for interference, added to the lip I.D.
• When selecting seal size, use the shaft O.D. as the seal I.D.
Then refer to size listings in the SKF Handbook of Seals for
determining the correct seal part number.
How to Subst i tute a New Seal for an Old Seal
When an exact replacement seal is not available, your best option
is substitution of a similar material and design. Refer to the SKF
Handbook of Seals guidelines on seal substitution. If the lip material
to match the old seal cannot be found in the size listings, refer to the
Recommended Operating Tables at the beginning of the Handbook.
Common lip material substitutes include:
• Nitrile instead of felt
• Nitrile instead of leather
• Polyacrylate instead of nitrile
• Another nitrile instead of the original nitrile
• Fluoroelastomer instead of polyacrylate
• Fluoroelastomer instead of silicone
The average of three equally spaced
measurements is the seal’s O.D.
(fig. 5b).
Note: Substitution may extend or shorten the seal life, depending
on the material chosen. Lip materials are covered in Chapter 4.
It is recommended that the compatibility tables shown in the SKF
Handbook of Seals be consulted for verification of material substitution.
47
Seal Selection (cont.)
Seal Selection Criteria
A
Factors to consider when selecting a seal for a particular application
(fig. 5c) include:
B
l
G
D
H
C
E
F
A variety of factors determine
proper seal selection (fig. 5c).
• Basic seal function
• Shaft surface finish (A)
• Shaft speed and direction (G)
• Shaft and bore conditions (B)
• Shaft eccentricity (E)
• Seal material/lubricant compatibility
• Underlip temperature (F)
• Contaminants (abrasiveness) (C)
• Pressure (internal/external) (I)
In many applications, seal life can be extended simply by substituting
the same size seal (O.D. and I.D.), but of slightly different design or with
a different lip material. A narrower seal width can usually be used (see
following “Seal Width vs. Seal Performance” section). The seal selected
must be able to meet the application’s requirements for operating
temperature, pressure, and other factors listed above.
100
80
PERCENT FAILURE
Single Lip vs. Double Lip Seals Test Results
DUAL LIP
SEAL
90
SINGLE LIP
SEAL
70
60
In its development of new seal designs, SKF has conducted extensive
testing. One series of tests has compared single lip with double lip
seals (fig. 5d). Test objectives were to determine:
50
• Does the double lip seal’s secondary (dust) lip help or hinder
the primary lip?
40
30
20
10
RELATIVE TIME TO FAILURE
(fig. 5d)
• How does the double lip seal’s overall performance compare
with that of the single lip seal?
During testing, these measurements were taken:
• Temperature vs. shaft speed.
• Dust ingestion vs. time.
• Peak performance vs. temperature rise.
Test results:
• The double lip seal failed at 270 hours.
• The single lip seal, tested under identical conditions, was still
running at 1254 hours.
• The single lip seal was proven to run four times longer than
the double lip seal.
48
• The single lip seal runs cooler.
Why Double Lip Seals Fail Faster
Lips create friction. Friction creates heat. So more lips mean more
heat. Heat causes the double lip seal to become hard and brittle
because the dust lip is lubricated less and can transfer its heat to
the main lip.
As the brittle secondary lip wears, it allows dirt to pass and pack
between the two sealing lips. This dirt builds and forces itself under the
primary lip. In a short time, the dirt will mix with the lubricant which
had been contained by the primary lip.
The mixture of lube and dirt becomes a lapping compound. Highly
abrasive, it wears the shaft, escapes past the seal lips and enters the
bearings to cause premature failure.
5
A Design Improvement—the Zero
Inter ference Auxiliar y Lip
SKF offers single as well as double lip designs. However, SKF has
found that its Waveseal design offers the attributes of double lip
capabilities with one significant difference.
The SKF Waveseal’s exclusive design utilizes a secondary lip that
excludes dirt without touching the shaft surface—it excludes dirt while
having zero interference. The Waveseal’s primary lip follows a wavy
path around the shaft, dissipating the heat over a wide area. The wave
lip retains and excludes at the same time, generating less friction,
torque and shaft wear.
The Waveseal design is detailed in Chapter 3.
Seal Width vs. Seal Per formance
Seal width is another factor to consider when selecting a replacement
seal. Seal width is the measurement of the axial dimension of the seal
case, not the seal lip length.
Since the width dimension doesn’t take lip design into account, it does
not provide a basis to explain the seal’s performance characteristics.
But it is important to note that, for proper seal operation, the case
must provide both an effective support for the seal lip and a good
surface area for proper installation. Today’s “narrow” seals—their cases
and their lip designs—are designed to satisfy these same requirements
(fig. 5e).
“OLD” DESIGN
“ N E W DESIGN”
Today’s “narrow” provide
performance effective seal lip
support and surface area for
proper installation (fig. 5e).
Certainly, lip dimension is a key factor in how—and how well—the seal
performs. This is the axial distance between the lip contact point and
the base of the flex thickness (the point of deflection takes place).
49
Seal Selection (cont.)
A longer lip often improves the seal’s capacity to compensate for
misalignments or eccentricities in the shaft surface. But lip length is
not necessarily related to seal width. Often, seal widths are increased
by changing the seal casing width without altering lip dimensions
in any way. These variables in dimensions have allowed seal
designers and manufacturers to inter-work them in producing higher
performance products—including those in more compact packages.
There are special applications where seal width cannot be reduced.
These often involve situations where seal widths are used as reference
points for other components. There also are applications where the
reduced width of a replacement seal will help extend shaft life. This is
accomplished by locating the contact point of the new seal away from
any damage on the shaft that may have been caused by the original
wider seal.
In general, use of a narrower seal as a replacement is very proper if it
is determined by a thorough examination of the application’s operating
conditions that all the other factors affecting the seal’s performance are
satisfied as well.
SKF’s WasteWatcherProgram
Another benefit of using narrower seals to replace original wider ones
is in inventory management. By stocking narrower seals of assorted
shaft and bore sizes while consolidating widths as much as possible,
inventory can be minimized while maximizing coverage.
SKF offers an inventory control system, called “WasteWatcher,” in
which distributors can consolidate replacement seals by I.D./O.D. sizes.
The program eliminates many stocking units that differ only by their
width dimensions. WasteWatcher also enables end-users to effectively
substitute single lip seals for comparable double lip designs.
Within distributors’ operating environments/performance requirements,
it is realized that the different “kinds” of seals that are used become
fewer in number over a period of time. As their sizes and application
requirements become more clearly defined, stocking units can become
further consolidated.
The “WasteWatcher” system is designed to streamline each end-user’s
inventory of replacement seals—to provide him with the seals and the
quantities he should stock for his market. The benefits to him, of
course, are excellent inventory cost controls and maximum efficiency
in use of inventory stocking space.
50
Chapter 5 Review
1.
_________________ is a premium lip material for the majority of sealing applications
today.
❑ a. LongLife fluoroelastomer
❑ b. Fluoropolymer (PTFE seals)
1. C
5
2. SKF seals are identified by an OEM part number or an SKF _________________ .
❑ a. stock number
❑ b. industrial part number
❑ c. drawing number
2. D
3. _________________ is an acceptable sealing lip material substitute for nitrile.
❑ a. Leather
❑ b. Felt
❑ c. Another nitrile
3. C
4. Selecting the right seal for a particular application depends on _________________ .
❑ a. size and speed
❑ b. pressure and temperature
❑ c. fluid compatibility
4. D
5. _________________ refers to the outside diameter of the shaft at the location where
the seal is mounted.
❑ a. Size bore
❑ b. Seal I.D.
❑ c. Seal width
❑ d. Shaft diameter
5. D
6. If the same size replacement is not available, _________________ .
❑ a. select a narrower seal
❑ b. select a wider seal
❑ c. select a different lip material
❑ d. either a. or b.
6. A
51
Chapter 5 Review (cont.)
7. Substitute lip materials will extend a seal’s life, no matter which material is chosen.
❑ True ❑ False
7. F
8. A combination seal or a double lip seal will always do a better job than a single lip design.
❑ True ❑ False
8. F
9. Seal width refers to the diameter of the hole in the housing into which the seal is fitted.
❑ True ❑ False
9. F
10. Fluoroelastomer is generally an acceptable sealing lip material substitute for silicone.
❑ True ❑ False
10. T
11. There are no acceptable sealing lip material substitutes for nitrile.
❑ True ❑ False
11. F
12. The temperature of the lubricant being retained is the only temperature
reading critical to seal selection.
❑ True ❑ False
12. F
13. When an exact replacement is not available, your best option is substitution
of a similar material and design.
❑ True ❑ False
13. T
14. In SKF’s single lip vs. double lip test, the single lip outlasted the double lip by
nearly 1000 hours.
❑ True ❑ False
14. T
15. SKF’s “WasteWatcher” seal inventory control system helps control costs
of replacement seals.
❑ True ❑ False
15. T
52
Chapter 6—Wear Sleeves
How Shafts Wear
Seals operate with a closely controlled interference at the interface.
Continuous contact between a rotating shaft and a seal produces shaft
polishing friction. Under normal conditions, the friction causes a slight
wear track on the shaft (fig. 6a). However, as operating conditions
begin to worsen, shaft wear can accelerate. Dust, heat, dirt, shaft
speed, lack of lubrication, and even a cocked seal can cause the seal
lip to groove the shaft. Mechanical eccentricities can cause direct,
metal-to-metal contact between the seal and shaft surface.
The ultimate result is a leak.
How to Identify Seal Worn Shaft Sur faces
W
O.D.
Shaft
As a seal continuously contacts
a rotating shaft, it creates shaft
wear (fig. 6a).
It’s not always easy to identify seal-worn shaft surfaces. The shaft may
be visibly scored or grooved. You can catch your fingernail in a wear
groove. A new seal that leaks soon after it’s installed is another telltale
sign of shaft damage.
6
The shaft surface can become so deeply grooved and worn that
a new seal will not eliminate leaks, nor compensate for the shaft
damage (fig. 6b).
Seal replacement does not solve the problem. The new lip will ride in
the rough, worn seal track and the new seal will leak and wear out
quickly.
Three solutions are possible:
• Reworking or metallizing the shaft surface at a machine shop—
high cost, requires hours of downtime.
• Replacing the shaft—Also expensive, with machine downtime.
• Installing a wear sleeve—Comparatively low in cost, virtually no
downtime, longer life.
Wear sleeves correct shaft damage instantly with the least amount of
downtime and cost. Wear sleeves require no special preparation or
machining of the shaft for installation. Applied over the damaged shaft,
a wear sleeve makes the shaft usable again. It eliminates shaft leaks
and smooths out damaged surfaces. And often the new shaft finish
created is better than the original.
Shaft surface can become so
deeply grooved and worn that a
new seal will not eliminate leaks,
nor compensate for the shaft
damage (fig. 6b).
SKF offers two types of wear sleeves: Speedi-Sleeves ®, for nominal
shafts .472” to 8.000” (12.00 to 203.20mm), and large diameter wear
sleeves, for shafts 8” to 45” (203.20 to 114.300mm). Made of
carbon steel and chrome-plated, the wear sleeve resists corrosion
in a wide range of applications.
53
Wear Sleeves (cont.)
Speedi-Sleeves ®
The Speedi-Sleeve is a cost-effective alternative to resizing,
metallizing or replacing the severely damaged surface because it
installs easily, without excessive machine downtime (fig. 6c).
Speedi-Sleeve is a highly engineered component, precision
manufactured of 300 series stainless steel. Its surface is factory
finished to 10-20 micro inch Ra (.25 to .50μm), with no machine
lead, and requires no expensive shaft preparation or machining before
installation. Once in place on the shaft, Speedi-Sleeve provides a
sealing surface that is superior to most original shaft finishes and
materials.
Speedi-Sleeve installs easily,
without excessive machine
downtime (fig. 6c).
Typically, when a wear sleeve is installed over the shaft, the
new surface is thicker and requires a larger-sized seal. The wall of the
Speedi-Sleeve is so thin that the original size seal can still be used. Its
stainless steel construction provides a surface that can outlast the
original shaft material.
Each sleeve is built with a removable flange and includes a special
tool for installation. This tool is placed over the Speedi-Sleeve. Both the
tool and sleeve are tapped into position on the shaft. The flange allows
the sleeve to be pulled on instead of pushed on, eliminating sleeve
distortion.
When the Speedi-Sleeve is in position, the tool slides off easily. The
flange can be left intact, or cut and peeled off along a pre-cut line.
It takes only a few Speedi-Sleeves to meet the needs of even the
biggest operators. In most cases, there is no need to stock more than
one size sleeve for each seal application or location.
Averaged caliper measurements
of shaft diameters at three positions
will compensate for out-of-round
conditions (fig. 6d).
Speedi-Sleeve Size Selection
Correct Speedi-Sleeve size selection requires that three measurements
of shaft diameter be taken and averaged. Use a caliper and measure
at three positions: noon and 6 o’clock, 2 and 8 o’clock, and 4 and 10
o’clock. Take these measurements at a point on the shaft ahead of the
wear path. Find the average of the three readings.
The average will compensate for out-of-round shaft conditions as
well as indicate the approximate shaft diameter (fig. 6d). When that is
determined, refer to the SKF Handbook of Seals to select the correct
Speedi-Sleeve part number.
54
Speedi-Sleeve Installation
Speedi-Sleeves are available for shaft diameters ranging from .469”
up to 8.005” (11.91 to 203.33mm). Each Speedi-Sleeve kit contains a
disposable installation tool and every box is marked with the shaft
range for proper selection.
Follow these guidelines for proper Speedi-Sleeve installation:
1. Clean the surface where the seal contacts the shaft.
File down and polish any burrs, nicks or rough spots.
Make sure the end is free of nicks and burrs.
2. Measure an unworn portion of the shaft where the sleeve
will be positioned. Do not install Speedi-Sleeve over keyways or splines unless their diameter is under nominal
shaft size. Measure in three positions and average the
reading, in case the shaft is out of round. If the average
diameter is within the range for a given Speedi-Sleeve,
there is sufficient press-fit built into the sleeve to keep it
from sliding or spinning. No cement is necessary.
Place flanged end of Speedi-Sleeve
onto shaft first. (fig. 6e).
6
3. If the groove does not require filling, optionally a light
layer of non-hardening sealant can be applied to the inner
surface of the sleeve.
4. If the shaft is deeply scored, fill the groove with powdered
metal epoxy type filler. Install Speedi-Sleeve before the
filler hardens.
5. Speedi-Sleeves are wide enough to cover the wear pattern
of both standard and wider combination seals. Where extra
wide combinations are encountered, a second sleeve can be
installed to butt against the first. The flange is then peeled
off to provide the clearance necessary for the seal housing
to slide into place. The Speedi-Sleeve installation flange can
be left in place unless it could prevent oil from reaching the
seal lip.
6. Determine how far back the sleeve must be positioned to
cover the old seal wear tracks. Measure to the exact point,
or mark directly on the shaft surface (fig. 6e).
7. The sleeve must be placed over the worn surface area, not
just bottomed or left flush with the end of the shaft.
…then apply the installation
tool over the sleeve and
against the flange… (fig. 6f).
55
Wear Sleeves (cont.)
8. Drop the Speedi-Sleeve into the end of the installation tool so
only the flange end projects (fig. 6f). The flange end of the sleeve goes
on the shaft first. Gently tap the center of the tool using a soft face
hammer or mallet until the sleeve reaches the previously marked
or pre-measured point on the shaft (fig. 6g).
9. Speedi-Sleeves may be installed to any depth required (refer to SKF
Handbook of Seals). If the installation tool supplied with sleeve is too
short, a length of pipe with a squared-off, burr-free end can be
substituted if its I.D. matches the kit installation tool.
…then gently tap center of tool
using soft-face hammer or
mallet until sleeve reaches
desired point on shaft (fig. 6g).
10. Inside pipe diameters should be larger than the shaft by:
Shafts less than 3” (75mm): 1/32” to 1/8” (.8mm to 3.2mm)
Shafts 3” to 6” (75-150mm): 1/32” to 3/16” (.9mm to 4.8mm)
Shafts more than 6”: (150mm) 3/64” to 7/32” (1.2mm to 5.6)
The installation tool correctly places the sleeve on the shaft to the
required installation depth (intermediate values can also be obtained by
pressing the sleeve on more or less as required).
11. If clearance is needed, the Speedi-Sleeve flange can be removed
easily with side cutters and carefully pried away from the sleeve. Bend
flange back and forth until flange cracks at tear groove. The flange will
peel away from sleeve surface along a precut line (fig. 6h). Be careful
nothing scratches the sleeve surface.
When Speedi-Sleeve is in position,
flange can be removed (fig. 6h).
Large Diameter Wear Sleeves
Large diameter wear sleeves correct damaged shafts from 8” to 45”
(203.20 - 1143.00mm) (fig. 6i). Though they function the same as
SKF Speedi-Sleeves, these sleeves are designed and built for heavyduty, large shaft applications. Installed over a seal grooved shaft, the
sleeve provides a positive sealing surface and reinforced protection.
They are available with or without an installation flange. They also
resist wear and corrosion, especially in contaminated environments.
SKF Large diameter wear sleeve
(fig. 6i).
56
SKF large diameter wear sleeves are custom-made from high quality
cold-rolled steel, SAE 1005-1020. The sealing surface is machined
and hard chrome-plated to provide a strong, corrosion-resistant
sealing surface. The standard thickness of the sleeve is 0.094”
(2.4mm). Other materials and thicknesses are available on a
quote basis.
Two styles of large diameter wear sleeves are available.
Style 3
Style 3 is designed with a flange for final positioning on the shaft
(fig. 6j). Actual sealing surface width is .250” (6.4mm) narrower than
overall sleeve width.
LDSLV3
Style 4
Style 3 features a flange for
pull-on installation (fig 6j).
Style 4 is designed without a flange (fig. 6k). It is used where space
restrictions limit the width or prohibit the use of a flange.
Large Diameter Wear Sleeve Installation
Large diameter wear sleeves are designed for heated, slip-fit
installation. A bearing heater (either hot air, hot oil or electric induction)
is used to bring the sleeve to about 350°F (176°C). Even with heating,
the sleeve may not position itself correctly and would then require
pushing or pulling on the flange.
LDSLV4
6
Style 4 is ideal where space
prohibits use of a flange (fig. 6k).
While a large diameter wear sleeve will increase shaft life and eliminate
leaks, it also increases the shaft diameter. When considering seals and
sleeves for a large shaft, choose one of two options:
• Machine the shaft before installing the sleeve to .188”
(4.8mm) under original size. The resulting sleeve O.D. will
allow use of the original size seal.
• Increase the seal size. No shaft machining is required.
Use seals designed for shafts .188” (4.8mm) larger than
the original.
Original
Option I
Option II
D.
14.000”
B.
Seal no.
1181640
Seal no.
1200560
Seal no.
1181640
A.
C.
Shaft 11.812” 11.812” Sleeve Shaft 12.000” 11.625” Sleeve Shaft 11.812”
Style 3
Sleeve
With flange
.094”
Style 4
Sleeve
.094”
Without flange
Unlike Speedi-Sleeve, adding an LD sleeve requires either reducing the shaft
diameter to compensate for the sleeve thickness or using a different seal sized
for the nominal sleeve outer diameter.
57
Chapter 6 Review
1. The Speedi-Sleeve is an ultra-thin wall made of _________________ that repairs
grooved shafts.
❑ a. bronze
❑ b. zinc
❑ c. stainless steel
❑ d. magnesium
1. C
2. The flange allows the Speedi-Sleeve to be _________________ eliminating
sleeve distortion.
❑ a. pushed on
❑ b. pulled on
❑ c. either of the above
2. B
3. SKF’s Large Diameter Wear Sleeves _________________ .
❑ a. repair damaged shafts 8” (203mm) and larger
❑ b. are built for heavy-duty applications
❑ c. provide high quality sealing surfaces and improved seal performance
3. D
4. If the shaft is deeply scored, you should fill the groove with _________________ .
❑ a. powdered metal epoxy type filler
❑ b. non-hardening sealant
❑ c. grease
❑ d. SAE 30 oil
4. A
5. A Large Diameter Wear Sleeve _________________ the diameter of the shaft.
❑ a. reduces
❑ b. increases
❑ c. will never change
5. B
6. When considering seals and wear sleeves for a large diameter shaft,
it is possible to _________________ .
❑ a. machine the shaft to a reduced diameter for use with the wear sleeve
and original size seal.
❑ b. apply the .094” thick (2.4mm) wear sleeve and use a larger sized seal.
58
6. C
7. When the Speedi-Sleeve is in position, the flange can be left intact,
or cut and peeled along a precut line.
❑ True ❑ False
7. T
8. More than one Speedi-Sleeve size is usually required for each seal application.
❑ True ❑ False
8. F
9. While the Speedi-Sleeve repairs damaged shafts, it is inexpensive and
requires little machine downtime.
❑ True ❑ False
9. T
10. Speedi-Sleeve’s wall is so thin that the original size seal can still be used.
❑ True ❑ False
10. T
6
11. Speedi-Sleeves cannot cover the wear pattern of wider combination seals.
❑ True ❑ False
11. F
12. Large Diameter Wear Sleeves are designed for heated, slip-fit installation.
❑ True ❑ False
12. T
13. Proper Speedi-Sleeve size selection requires that seven measurements can be taken
and averaged.
❑ True ❑ False
13. F
14. Speedi-Sleeve’s stainless steel construction provides a surface that can outlast the
original shaft material.
❑ True ❑ False
14. T
15. The most economic repair option for a worn shaft seal is to install a wear sleeve.
❑ True ❑ False
15. T
59
The shaft corners
must be burr-free
15-30˚
Chapter 7—Shaft
and Bore Conditions
In addition to application parameters and environmental factors, shaft
and bore specifications are important to proper seal selection.
Shaft Conditions
fig. 7A
.070 - .120 INCH
(1.7B - 3.05mm)
Shaft surfaces must be
smooth and free of nicks
and rough spots
Sealing Sur face Requirements
SKF produces thousands of seals in designs, sizes and lip materials to
meet the most severe operating conditions.
For proper seal performance, three factors must be considered:
1. The shaft surface has no machine lead (grooves running
diagonally toward or away from the sealing lip).
2. The entrance edge is chamfered or rounded.
3. The surface finish is 8-17 micro inch Ra (.20 μm to .43μm).
Shaft Requirements
fig. 7B
R.125 INCH
(3.18mm)
Burr-free radius alternatives
can also be used (fig. 7b).
A
A burr-free chamfer (fig. 7a) or radius (fig. 7b) is required as
illustrated (c = chamfer depth).
Because the seal’s inside diameter is difficult to measure and varies
with seal designs, the shaft diameter for which the seal was designed
is used as the cataloged inside dimension.
Shaft Eccentricity
Two types of shaft eccentricity affect seal performance. They are:
B
A dial indicator is used to
measure STBM (fig. 7c).
Dynamic run-out is also measured
using a dial indicator (fig. 7d).
60
• Shaft-to-bore misalignment (STBM)—The amount by which the
shaft is off center, with respect to the center of the bore. This
somewhat common occurrence is caused by machining and assembly
inaccuracies. To measure, attach a dial indicator to the shaft (between
the shaft and bore), rotate the shaft and read the indicator (fig. 7c).
• Dynamic run-out (DRO)—DRO is the measure of the amount
by which the shaft does not rotate around the true center. The
motion away from the center may be in more than one direction.
Misalignment, in-line boring tolerances, shaft bending, lack of shaft
balance and other manufacturing inaccuracies are common causes.
To measure, slowly rotate the shaft and calculate total movement
of an indicator attached to the bore and held against the shaft’s
side (fig. 7d).
For specific limitations on both shaft-to-bore misalignment and
dynamic run-out and the total eccentricity (combined STBM and DRO
readings) indicator, refer to the SKF Handbook of Seals.
Shaft Speed
Maximum speeds for effective seal operation depend on shaft finish,
pressure, temperature, eccentricity, lubricant or fluid being retained,
seal type and other conditions. For example, shaft speeds may be
increased (not to exceed manufacturer upper limit) when shaft finish
is improved or eccentricity (run-out) is reduced.
The surface speed at the contact point between the seal and shaft as
measured in fpm (feet per minute) or mpm (meters per minute) or fps
(feet per second) or M/S (meters per second) is generally a better seal
selection guide than rpm (revolutions per minute).
Shaft Tolerance
It is important to note that machinery built with inch vs. metric
dimensions may use different tolerance standards. In general, the inch
(RMA) system uses a ‘floating’ range based on the nominal shaft diameter plus or minus some value depending on the base size. With the
metric (ISO) standard, the tolerances for shafts are applied as a plus
zero / minus value (typically ISO h11). While the lip interference
of radial lip seals is relatively less sensitive to shaft diameter variations,
the best recommendation is to specify the correct size for the
tolerancing system used. Refer to the SKF Handbook of Seals for
tolerance tables and other details.
7
Recommended Shaft Materials
Seals perform best on medium carbon steel (SAE 1035, 1045) or
stainless steel surfaces. Properly finished ceramic-coated and chromeplated or nickel-plated surfaces are also acceptable. Brass, bronze and
alloys of aluminum, zinc, magnesium or plastics are not recommended.
Surface should be hardened to Rockwell C30 or higher to prevent
handling damage or abrasive wear.
Recommended Shaft Finish
Shaft finish is critical to the proper functioning of a lip-type seal (fig.
7e). It is important to note that not all shaft finishes are good ones.
An improper shaft sealing surface will not allow the seal to function
properly. Generally, the shaft surface should be smooth enough to
maintain effective contact with the seal lip. But it also must be rough
enough to form lubricant holding pockets, without causing excessive
seal wear.
A new shaft with the proper finish is
shown on the left; normal shaft wear
is shown on the right (fig. 7e).
Machine lead is always present after the shaft has been machined to
size on a lathe. It is necessary to dress the shaft surface to remove the
lead introduced during the machining operation.
61
Shaft and Bore Conditions (cont.)
Seal and original equipment (OE) manufacturers agree the following
shaft conditions must be met:
• Shaft finish should fall between 8 and 17 micro inch Ra
(.20μm to .43μm).
• Shafts should be ground with mixed number rpm ratios.
• Plunge grinding is the preferred method
• The shaft finish should be free of machine lead spiral marks that
can cause lip damage and auguring out of the lubricant.
• The entrance edge should be chamfered or rounded.
*In addition to the finish roughness, parameters related to texture and other factors
are important to optimum seal performance. Refer to the SKF Handbook of Seals for
further information.
To maintain a smooth sealing surface, remove any surface burrs, nicks,
rough spots or grooves. Such imperfections can damage the lip seal as
it slides on the shaft.
Pl u n g e G r i n d i n g
Plunge grinding is the recommended method for shaft finish.
It produces short, parallel grooves or pockets which hold lubricants
without letting them escape (fig. 7f). Other methods, while smooth
enough, may create shaft lead or not completely remove lead
patterns that may be present.
Plunge grinding is the recommended
method for shaft finish (fig. 7f). (50x
magnification)
The wheel used to grind the shaft moves straight into rather than
across the surface. This action eliminates any axial movement of the
grinding wheel on the shaft surface and prevents spiral grooves
(machine lead) that may promote seal leakage.
For plunge grinding to be effective, a cluster head dressing tool must
be used. Work at a slow pace (three inches per minute), use a mixed
number ratio between grinding wheel rpm and shaft rpm, and take
shallow cuts (two thousandths the first pass, one thousandth the
second). Run the grinding wheel until it sparks out.
Checking the Shaft for Sur face Roughness
Seal manufacturers agree that the optimal shaft surface range
is 8 to 17 micro inch Ra (.20μm to .43 μm), with no machine lead.
A Talysurf machine can check the surface and calculate average
surface roughness.
The average surface roughness appears in a digital readout. A chart
provides a “picture” of the actual shaft surface. However, even if the
resulting finish falls within the acceptable range, machine lead may
still be present.
62
Testing for the Presence of Machine Lead
Testing the shaft surface for machine lead can be done simply and with
a minimum of tools. The most effective method requires a 36 inch
(914.4mm) length of cotton quilting thread, a one ounce weight and
silicone oil.
Mount the shaft in a chuck so the shaft surface is level. Lightly coat the
shaft with oil. Suspend the weight on the thread as shown here.
Rotate the shaft at approximately 60 rpm. If the thread moves along
the shaft, machine lead is present (fig. 7g).
Bore Requirements
Testing the shaft surface for machine
lead is a simple process requiring a
minimum of tools (fig. 7g).
The lead corner, or entering edge, of the bore should be chamfered
with a 15/30 degree angle and free of burrs. The inside corner of the
bore should have a maximum radius of .031 (.79mm). This will help
prevent seal damage during installation. Chamfer length should be
.060” to .090” (1.50 to 2.29mm); see fig. 7h.
Bore Tolerance
Similar to shafts, the inch (RMA) system for seal bores also uses
a “floating” range based on the nominal diameter plus or minus
some value depending on the base size. With the metric (ISO)
standard however, the tolerances for bores (typically ISO H8) are
applied as a plus value/minus zero. Unlike shafts and seal lips, the
bore fit for seals can be significantly affected by the tolerance applied
to the hardware. For the best results, the correct bore diameter
for the tolerance system used should always be observed.
7
R .031
(0.79 mm)
.060 - .090
(1.52 - 2.229 mm)
Refer to the SKF Handbook of Seals for tolerance data and further
information on housing bores.
15-30
FINISH 100 microinch
OR LESS
Ra
(fig. 7h)
(2.5 micrometer)
Bore Hardness
No specific Rockwell hardness is recommended. Bore hardness need
only be high enough to maintain interference with the seal’s outside
diameter.
Bore Material
Ferrous and other commonly used metallic materials (like aluminum)
are acceptable for the bore. Bore material must be compatible with the
seal type used; if an aluminum bore is used, thermal expansion may
have to be considered.
63
Shaft and Bore Conditions (cont.)
Bore Finish
A bore finish of approximately 100 micro inch Ra (2.54 μm)
or smoother (100 to 200 micro inch Ra [2.54μm to 5.08μm] for
aluminum), should be maintained to avoid leakage between the seal
outer diameter and housing. An inside corner that is too rounded or
a corner with too large a radius can cause the seal to distort when
pressed into the bore.
SKF applies a coating of Bore-tite to the O.D. on selected metal-clad
seals on production quantities at the factory. Seals without Bore-tite
can be improved by applying a non-hardening, pliable sealant to the
O.D. prior to installation.
64
Chapter 7 Review
To take this test, simply place a card or sheet of paper under the first question.
After you’ve read it (and answered it to yourself) slide the paper down below the next
question. The correct answer to the first problem will appear directly to the right
of the new question. Be sure not to skip any questions.
1. To help ensure proper seal performance, the shaft _________________ .
❑ a. entrance edge should be chamfered or rounded
❑ b. surface finish should be 8-17 micro inch Ra (.20μm to .43μm)
❑ c. surface should have no machine lead
1. D
2. _________________ refers to the amount by which the shaft does not
rotate around the true center.
❑ a. Shaft-to-bore misalignment
❑ b. Dynamic run-out
❑ c. Shaft diameter
2. B
3. The recommended method for obtaining an optimum shaft finish is
_________________ .
❑ a. paper polishing
❑ b. roto preening
❑ c. plunge grinding
❑ d. diamond burnishing
7
3. C
4. Seals perform best on Rockwell C30 medium carbon steel
(SAE 1035, 1045) or _________________ .
❑ a. stainless steel
❑ b. aluminum
❑ c. bronze
❑ d. zinc
4. A
5. To assure a smooth sealing surface, the shaft should be ground with
_________________ rpm ratios.
❑ a. even number (2 to 1)
❑ b. odd number (3 to 1)
❑ c. mixed number (3.5 to 1)
5. C
65
Chapter 7 Review (cont.)
6. Spiral grooves (machine lead) may promote seal leakage.
❑ True ❑ False
6. T
7. Tumbled stone finishing provides a positive solution to machine lead.
❑ True ❑ False
7. F
8. Shaft speeds should be reduced when shaft finish or eccentricity (run-out) is reduced.
❑ True ❑ False
8. F
9. Revolutions per minute (rpm) is a better seal selection guide than the surface speed
at the contact point between the seal and shaft (fpm: feet per minute).
❑ True ❑ False
9. F
10. The shaft surface should be smooth enough to prevent excessive seal wear, but
“rough” enough to form lubrication holding pockets.
❑ True ❑ False
10. T
11. Ferrous and other commonly used metallic materials (such as aluminum) are
acceptable bore materials.
❑ True ❑ False
11. T
12. Roto preening is recommended to dress the shaft and remove lead introduced during
the machining operation.
❑ True ❑ False
12. F
13. Imperfections such as surface burrs, nicks or rough spots on the shaft surface can
damage the lip as it slides on the shaft.
❑ True ❑ False
13. T
14. Bore material must be metallurgically compatible with the seal type that is used.
❑ True ❑ False
14. T
15. Bore-tite on a metal clad seal’s O.D. efficiently fills major bore imperfections.
❑ True ❑ False
15. F
16. It is acceptable to use inch sized seals in metric sized equipment.
❑ True ❑ False
16. F
66
Chapter 8—Installation
The seal is ready to be installed in the bore once the shaft and bore
have been checked and cleaned, and the seal has been pre-lubricated.
Be sure to keep the work area and tools clean. Do not unbox the seal
until immediately prior to installation. Be careful not to introduce any
contaminants into the seal or bearing cavity (fig. 8a).
Inspect the Shaft and Housing
Remove any burrs or nicks which could damage the seal lip or score
the O.D. Make sure that the housing and shaft have a smooth,
chamfered edge.
Pre-Lubrication
The lip of the seal must be pre-lubed with clean lubricant
before the seal is installed. The seal O.D. of metal cased seals can
be oiled or installed dry. However, rubber O.D. seals must always be
pre-lubricated. This step is important because pre-lubrication aids
mounting and provides a film on which the seal rides until there is
ample lubricant in the seal cavity.
The best pre-lube to use is the lubricant being retained. This
precaution can prevent any problems occurring by mixing two different
lubricants together.
Before installing the seal, check to see
that the shaft and bore are cleaned and
the seal is pre-lubricated (fig. 8a).
Choosing an improper pre-lube could damage the seal lip, causing it to
shrink, swell or soften. By using the same lube as that being retained,
you can eliminate the possibility of selecting a lubricant with a limit of
200°F (93°C) for an application where the temperature might run as
high as 250°F or 300°F (121°C to 149°C).
8
Proper Installation Procedures
The first step in installation is to confirm that the seal meets the
specific application requirements. Always be sure to check the
dimensions, orientation of lip, helix direction, and condition of lip
before pre-lubing.
To assist in mounting, always be sure to lube the O.D. of rubber
covered seals. A light lube can also assist in the mounting of metal
clad seals.
Tools
The best method for seal mounting is to use an arbor or hydraulic
press that applies uniform pressure against the seal. Always use a
proper size tool to apply installation force. If a press is not available or
not practical, use the second best alternative—a round tool. A bearing
cup is excellent. If it must follow the seal into the bore, it should be
slightly smaller than the outside diameter of the seal. An O.D. .010”
(.25mm) smaller than the bore is ideal.
67
Installation (cont.)
For best results, the center of the tool should be open so pressure is
applied only at the outer edge.
The tools used to install seals can often affect seal performance.
For instance, a screwdriver may easily cut the seal lip, but make
the damage invisible to the eye. Even blunt-end drifts can damage
the seal case or distort the seal from its proper working position.
Ideal Installation Conditions—Arbor Press
This hydraulic press method is best for providing the uniform pressure
necessary to overcome seal O.D. press fit, usually 0.004 to 0.008
inches (0. 102mm to 0.203mm) larger than the bore (fig. 8b).
The arbor press installation method
provides the uniform pressure needed
to overcome seal .D. press fit (fig. 8b).
Before installation, pre-lube the seal. To protect the seal outer shell,
apply pressure through an installation collar that contacts the seal near
the O.D. and has a relieved center to avoid pressure on the I.D. of the
seal face.
When installing the seal in a step bore, be careful not to squeeze or
crush the seal case. When installing in a “through” bore, apply pressure
through a steel plate or plug larger than bore diameter (to set the seal
perpendicular to the shaft).
Alternative Installation
Method—Wooden Block Installation
Use of a wooden block as an installation tool is acceptable when the
seal is to be installed flush with a housing and no arbor press is available.
Before installation, pre-lube the seal. Use the flat surface of the woodblock to press the seal in place. A steel hammer can be used to apply
force to the wood block and to overcome the seal’s press fit diameter.
When using the wooden block
installation method, apply force
in the area over the center of
the seal (fig. 8c).
Apply force evenly across the back of the seal. That is, avoid forcing
one side of the seal first, thus cocking the seal (fig. 8c). Apply no direct
force to the seal I.D.
Whatever tool is used, remember that seating force must be applied
and spread out around the entire circumference of the seal. A direct
blow on one side of the seal distorts the shell and can cause the lip
to be pressed against the shaft. This action produces increased
friction between the lip and the shaft surface.
If installation pressure is applied to the seal’s inside diameter, the shell
is forced upward, lifting the lip from the shaft surface. If the seal is
cocked—not perpendicular to the shaft and bore—the result will be
too much contact on one side, and not enough on the other.
Careless installation is one of the most common reasons for seal
problems. The end-user can prevent these problems by reviewing
and following the recommendations on the opposite page.
68
For best seal per formances, use:
• Arbor or hydraulic press
• Wooden block
• Soft-faced hammer or mallet
Installation tools in order of preference:
• Tools tailor-made for seal installation
• Standard driving plug
• Old bearing cup
• Wooden block
Sealing damage may result when using:
• Steel hammer
• Drift or punch
• Chisel or screwdriver
• Direct hammer blows on the face of the seal
• Starting seal into the bore at an angle (cocked)
I n s t a l l a tion C h e c k l i s t
1. Check the bore. Remove any burrs from the leading edge.
Be sure there is a rounded corner or chamfer (fig. 8d).
8
2. Check the shaft. Remove burrs, surface nicks, grooves and spiral
machine marks (machine lead).
3. Check the shaft end. Remove burrs or sharp edges. If the shaft
enters the seal against the sealing lip, its end must be chamfered
or a special installation tool must be used.
4. Check splines and keyways. Sharp edges should be covered
with a lubricated assembly sleeve, shim stock or tape to protect
the seal lip.
5. Check the dimensions. Make sure that shaft and bore diameters
match those specified for the seal selected.
Remember to check shaft and bore
surfaces and pre-lube the seal
before installation (fig. 8d).
6. Check for part interference. Watch out for other machine parts that
might rub against the seal and cause friction and damaging heat.
7. Check the seal. Damage may have occurred before installation.
A sealing lip that is turned back, cut or otherwise damaged should
be replaced.
69
8. Check seal direction. Make sure the new seal faces in the same
direction as the original one. Generally, the lip faces the lubricant
or fluid being retained.
9. Use the correct installation tool. Press-fitting tools should have an
outside diameter approximately .010” (.254mm) smaller than the
bore size. For best results, the center of the tool should be open
so that pressure is applied only at the outer edge.
10. Pre-lubricate the sealing element. Before installation, wipe the
sealing element and shaft with the lubricant being retained.
Rubber O.D. seals must be completely lubricated.
11. Never hammer directly on the surface of the seal. Use proper
driving force such as a soft face tool, arbor press or soft workpiece
(wood). To avoid cocking the seal, apply force evenly around the
outer edge.
12. Position the seal properly in the housing and inspect for alignment
and installation damage.
Post-Installation Tips
When painting, be sure to mask the seal. Avoid getting paint on the lip,
or the shaft where the lip rides. Also, mask the vents so they will not
become clogged.
If paint is to be baked or the mechanism otherwise subjected to heat,
the seals should not be heated to temperatures higher than their
materials can tolerate.
In cleaning or testing, do not subject seals to any fluids or pressures
that could damage them. Check the Compound Selection Chart in
the SKF Handbook of Seals when in doubt. Improper installation
procedures will result in early seal failure. Three of the most common
installation errors are detailed below.
Common Installation Errors Damage from
Shaft Burr
Symptoms
Shaft burr damage is evidenced when early lip leakage signals there
is a cut (usually visible) in the seal lip.
Causes
A cut on the seal lip can be
caused by shaft burrs (fig. 8e).
70
This cut was probably caused by a burr on the shaft which caught and
tore the seal lip. A burr on the spline or keyway of the shaft may have
caught the seal lip (fig. 8e). It also could be caused by not chamfering
the leading edge of the shaft or bore.
Corrective Actions
Inspect the mating surfaces of the bore and shaft. Remove any burrs
and nicks from the bore and shaft. Tape the keyway or spline, then
lubricate it. Chamfer the leading edges of the bore and shaft. Pre-lube
the seal to ease its installation over the shaft. Use a cone or sleeve
made from shim stock to slide the seal over the shaft.
Common Installation Errors—Cocked Seal
Symptoms
Markings can be tell-tale signs that the seal was cocked (tilted) during
installation.
Light scratches on the front of the seal would appear when the case
was first inserted. Since the seal was cocked, it takes additional force
to seat the back half. This extra force causes heavier markings on the
back of the seal (fig. 8f).
Other symptoms include early lip leakage, high or low wear on the
lip or wide wear on the shaft.
Markings on the case or metal insert
signal the seal was cocked during
installation (fig. 8f).
Causes
A seal can be cocked if uneven pressure was applied during installation
or if the entering edge of the bore was not chamfered. Also, the
housing could have been cocked during installation. This can occur
during arbor press assembly if foreign material gets under the housing.
8
Corrective Action
If the seal is cocked, you must remove the cocked seal and put in a
new one, applying uniform force to the seat during press fit installation.
Be sure to use the correct tools and procedures to be sure the new
seal is straight.
Common Installation Errors—
Damaged Seal Case
Symptoms
Immediate lip leakage usually occurs when the case is damaged,
out of round, or bent.
Causes
This can occur when pressure is applied incorrectly or unevenly during
installation, or if improper tools that can damage the seal case are
utilized. After the seal bottoms out in a step-bore, continued pressure
will bend the case inward (fig. 8g).
Uneven installation pressure
can damage the seal case,
causing lip leakage (fig. 8g).
71
Corrective Actions
Use the correct tools and procedures to apply uniform pressure to
press fit the seal in the housing.
Large Diameter Seal Installation
Installation of a large diameter seal follows the same procedures
as those used in standard seal installation. Follow these steps:
• Check the bore, shaft, shaft ends, splines and keyways, for
imperfections, dirt and anything that shouldn’t be there.
• Check dimensions. Be sure the correct seal size has been selected.
• Check for parts interference. Watch out for metal-to-metal contact
between the seal shell and shaft surface.
To install a large diameter
seal, tap around the seal in the
sequence shown above (fig. 8h).
• Check the seal. Is it the right style for the application?
• Check seal direction. The seal lip should be pointed toward
the lube for retention, or away from the lube for dirt exclusion.
• Pre-lube the sealing element. Always use the same lubricant
as the one used in the application.
• Position the seal properly. Be sure it sits squarely in the bore.
During installation, never hammer directly on the seal. Because
of their size, it is often not possible to apply uniform pressure across
the seal at one time.
For f lush installation:
Use a board or wooden block to progressively tap the seal into the
bore. A little at a time, gradually ease the seal into the bore. Gently tap
at 9 o’clock, 3 o’clock, 12 o’clock and 6 o’clock positions to avoid cocking
the seal (fig. 8h).
Large Diameter Spli t Seal Installation
A large diameter split seal is correctly installed by following these steps:
• Lightly lubricate the seal’s O.D. and inner lip.
• Apply the seal around the shaft, positioning it at the desired
location with the butt ends of the seal at the 12 o’clock position.
HS8
Connect the split seal’s spring after
the seal is placed around the shaft
(fig. 8i).
72
• Make the spring connection (see following section for details) (fig. 8i).
• Tap the seal in place, alternately striking lightly around
its circumference.
• Install the cover plate.
Spli t Seal Fi tting
All HS seals require a cover plate (fig. 8j). The cover plate provides
the compression fit necessary to ensure a leakproof seal. It should be
thick enough .250” to .500 inches (6.3mm to 12.70mm) not to bend
or distort. The cover plate should also be secured by bolts or studs no
more than 6” (152.40mm) apart on the bolt circle. Splitting the cover
plate in two or more sections will make seal replacement easier,
particularly in confined areas.
To block surges of lubricant toward the seal from the inside and to
protect the seal from damage from the outside, the cover plate I.D.
should be as close as practical to the shaft. Generally, 1/4” (6.3mm)
over shaft size is sufficient for clearance in the presence
of moderate shaft misalignment and run-out.
If supplementary sealing is required but it is impractical to machine
the original housing, the seal cavity may be incorporated into a new
plate which is then bolted into place.
Procedure
Cover plates ensure a
leakproof seal (fig. 8j.)
• Lightly lube seal O.D. and inner lip.
• Put seal around shaft.
• Install spring into its groove if required
• Make spring connection.
• Install butt-ends first at 12 o’clock position.
• Tap into place, alternately striking around seal.
• Install cover plate.
8
73
Spli t Seal Connectors
There are three types of stainless steel spring connectors
for SKF split seals:
• Control-wire
• Hook and eye
• Threaded
Control-Wire Connector
Making the split seal easy to install, the control-wire connector offers
these features, benefits and limitations:
The control-wire connector fits into
the core of the garter spring (fig. 8k).
• The connector wire slips into the core of the garter spring for
connection (fig. 8k).
• The Spring-Kover keeps the spring in place.
Of the three types of connectors, this provides the least secure spring
connection. The seal ends might not join completely due to the ease of
assembly feature.
It is recommended only for horizontal shafts running at speeds below
1500 fpm (7.62 m/s), retaining grease. It is used only with SKF’s HS7
seal design.
The hook and eye provides positive
spring connection on seals for larger
(18 diameter) shafts (fig. 8l).
Hook and Eye Connector
The hook and eye (fig. 8l) assembles easier than threaded connectors,
and provides a positive spring connection. It is used only on seals for
shaft diameters over 18.001 inches (457.23mm), or by special order.
Threaded Connectors
Threaded connectors provide positive
spring connection on seals for shaft
diameters under 18 (fig, 8m).
74
Most difficult to install of the three, threaded connectors (fig. 8m)
provide the most positive connection of the spring. They are used on
smaller seals, for shaft diameters up to 18 inches (457.22mm) or by
special order.
V-Ring Ins t a l l a t i o n
These step-by-step procedures will assure correct SKF V-Ring installation:
• Clean the shaft and counterface. Make sure there is no grease or oil on
the V-Ring’s shaft seating surface.
• Apply a light coat of molycote, grease or silicone oil to the counterface
or lip. This will minimize break-in wear as well as maximize the
V-Ring’s service life.
• Mount the V-Ring by hand. It should be stretched uniformly around the
shaft (it can be stretched up to 2 1/2 times its molded diameter).
• On shaft diameters over 19.685 inches (500mm), run a blunt tool
between the V-Ring and the shaft to assure uniform stretch. Make
sure the V-Ring is located clear of housings or projections.
V-rings should be selected for the shaft size being used and mounted
on the shaft based on the “B1” dimension, or distance from the rear
base of the ring to the surface its lip is contacting. It is called the
“width of seal” in the SKF Handbook. Other key installation dimensions
are the D2, or maximum gap between the shaft and housing and D3,
the minimum radial clearance around the V-ring.
B1
V-Rings should be mounted to their
“B1” dimension (fig. 8n).
While the V-ring can stretch to fit on the shaft, sometimes it is
necessary to cut the ring, fit it around the shaft and rejoin the ends.
It is possible to use cold or hot bonding methods, depending on the
operating conditions. SKF offers special instructions for bonding the
rings based on which compound is involved.
8
75
Chapter 8 Review
you’ve read it (and answered it to yourself), slide the paper down below the next question.
1 . The seal is ready to be installed in the bore when _________________ .
❑ a. the shaft and bore have been checked and cleaned
❑ b. the seal has been pre-lubricated
1. C
2. For best seal performance, use a(n) _________________ or soft-face hammer
for seal installation.
❑ a. screwdriver
❑ b. arbor press
❑ c. chisel
❑ d. steel hammer
2. B
3. Press-fitting tools should have an outside diameter approximately _________________
the bore size.
❑ a. .010” (.254mm) smaller than
❑ b. .010” (.254mm) larger than
❑ c. equal to
3. A
4. Seals which are to be flush with the outside of the housing can be pressed
in with a _________________ .
❑ a. drift
❑ b. punch
❑ c. block of wood
❑ d. chisel
4. C
5. The wrong installation tool can _________________ .
❑ a. cut the seal lip
❑ b. damage the seal case
❑ c. distort the seal
5. D
6. A sealing lip that is cut, turned back or damaged should be _________________ .
❑ a. repaired
❑ b. replaced
❑ c. cleaned
❑ d. chamfered
6. B
76
7. Careless installation is a common reason for seal problems.
❑ True ❑ False
7. T
8. In wooden block installation, the sealing force of the installation tool should be applied
uniformly across the seal case, not concentrated in the center.
❑ True ❑ False
8. T
9. A cocked seal is perpendicular to the shaft and bore.
❑ True ❑ False
9. F
10. Shaft and bore diameters should match those specified for the seal selected.
❑ True ❑ False
10. T
11. An arbor press does not apply uniform pressure against a seal.
❑ True ❑ False
11. F
12. A direct blow on one side of the seal distorts the shell and can cause the lip to be
pressed against the shaft.
❑ True ❑ False
12. T
13. The new seal should face the opposite direction of the original one.
❑ True ❑ False
8
13. F
14. Using the arbor press method to set the seal perpendicular to the shaft when
installing a “through” bore, apply pressure through a steel plate or plug larger than
bore diameter.
❑ True ❑ False
14. T
15. The best pre-lube to use is the lubricant being retained by the seal.
❑ True ❑ False
15. T
16. V-rings can not be stretched when installing them on shafts.
❑ True ❑ False
16. F
17. Control wire connections on HS7 split seals can be used for oil sealing applications
❑ True ❑ False
17. F
18. With V-rings, it doesn’t matter where they are positioned on the shaft so long as the
shaft diameter is correct.
❑ True ❑ False
18. F
77
Chapter 9—Troubleshooting
Preliminar y Sur vey
The best way to troubleshoot is to follow a sequence of steps that
should lead you to the problem.
• What was the seal supposed to do? How well has it done the job in
the past? If there is a history of failures, the problem may not be
caused by the seal itself.
• Was it the right seal? Check the seal’s part number and look up its
recommended applications. If the correct seal has been installed and
there is no history of repeated failures, the problem requires further
investigation.
• Pinpoint the source of the leak. It may be either an I.D. leak or an
O.D. leak. Also, find out when the leak first occurred and see if this
relates to a change in maintenance or operating procedures.
• In the case of exceptional seal wear, what is the cause of this wear?
To find out requires failure analysis.
Basic Steps in Analyzing Sealing System Failures
Follow these steps in determining why a seal has failed:
• Inspect the seal before removal to check the condition of the area,
note the amount of leakage that has occurred, and determine the
source of the leakage (fig. 9a).
Inspect the seal and check for signs
of failure (fig. 9a).
• Wipe the area clean and inspect to determine if:
- There are nicks on the bore chamfer,
- The seal is cocked in the bore,
- The seal was installed improperly,
- There is shaft-to-bore-misalignment,
- The seal is loose in the bore,
- The seal case is deformed, and/or
- There is paint on the seal.
• Rotate the shaft to determine if there is excessive end play
or excessive run-out.
If the leakage cannot be located, follow this procedure:
• Add ultraviolet dye to the sump or spray the area with white powder.
• Operate for 15 minutes.
• Use ultraviolet or regular light to check for leakage.
• Mark the seal location at 12 o’clock and remove it carefully.
Check for nicks on the bore chamfer.
78
With the seal removed, check for:
• Rough bore surface.
• Shaft cleanliness (is it clean and free of carbon?)
• Coked lube on the shaft.
• Shaft damage.
• Flaws or voids in the bore.
• Shaft corrosion.
• Shaft discoloration.
Identify the seal style and materials. Then inspect it for:
• Primary lip wear.
• Primary lip conditions.
• Seal O.D. wear/damage.
• Spring damage.
Proper Seal Measurement
Two of a seal’s measurements are its outer diameter (O.D.) and its
inner diameter (I.D.). To determine these, follow these procedures:
• To measure the O.D. of a seal, take three measurements equally
spaced around the outside of the seal. The average of the three is
the seal’s O.D (fig. 9b).
• A metal O.D. seal is generally 0.005 to 0.016 inches (0. 13mm
to 0.41mm) larger than the bore, for press fit.
• A rubber O.D. seal is generally 0.008 to 0.020 inches (0.20mm
to 0.51mm) larger than the bore, for proper compression and
interference fit.
The average of three measurements
around the outside of the seal is the
seal O.D. (fig. 9b).
9
• The inner diameter is more difficult to measure. Take about five
I.D. readings, average them and add an interference figure to the lip
I.D. to reach the approximate shaft I.D. (see Catalog 457010).
• Alternatively, use the shaft O.D. as the seal I.D. Then refer to size
listings in the SKF Handbook of Seals, for determining the correct
seal part number.
Common Sealing Problems
Common sealing problems, their causes and solutions, are detailed
below.
Hammer Damage
Visible dents on the seal back are
symptoms of hammer damage (fig. 9c).
Some obvious signs of hammer damage include visible dents on the
seal back, a distorted sealing element, or a garter spring that pops out
(fig. 9c).
79
Troubleshooting (cont...)
Causes
Such hammer damage can be caused by using a steel hammer on the
seal housing during installation.
Corrective Actions
A
Never hammer directly on the seal. Seals which are to be flush with
the outside of the housing should be pressed in with an installation
tool larger than the seal O.D. or with a block of wood. In this case it is
acceptable to use a steel hammer, a dead blow hammer or soft-faced
hammer on the wooden workpiece.
B
Shaft-to-bore misalignments (left)
and dynamic run-out (right) both
cause early lip leakage (fig. 9d).
When the blow is going through steel (such as a bearing ring), use
a soft-faced or dead-blow hammer or mallet. This type of tool, like
a block of wood, absorbs the shock wave created by the tool’s impact.
A hammer blow without any material to absorb the shock wave can
dislodge the garter spring from its proper operating position. Once
the spring is out of position, the seal will fail. It may even interfere
with the action of the seal lip, or find its way into the bearing.
Shaft-to-Bore-Misalignment Dynamic Run-Out
STBM
Misaligned components in a power train
create Shaft to Bore Misalignment (STBM)
and leaks. The seal lip will appear worn
on one side and relatively untouched on
the other. Shaft alignment should always
be checked before installing a new seal
(fig. 9e).
Early lip leakage, excessive (uneven) lip wear on one side of the seal,
and/or excessive but consistent lip wear all around are symptoms of
shaft-to-bore-misalignment or dynamic run-out.
Causes
Shaft-to-bore-misalignment (STBM) is a condition of excessive
misalignment created by inaccurate machining, shaft bending, lack of
shaft balance or worn bearings (fig. 9d and fig. 9e). Dynamic run-out
(DRO) is a similar condition where the shaft does not rotate around
its true center (fig. 9d and fig. 9f).
If you find a leaking seal with a wide wear band on one side, but a
narrow band on the other, you can suspect high STBM (unless O.D.
markings indicated the seal was cocked). The lip area with the greatest
wear indicates the direction of shaft misalignment.
DRO
Dynamic Run Out (DRO) is the result of a
bent, unbalanced or misaligned shaft. The
sealing lip will be severely worn around
the entire diameter. A dial indicator
attached to the bore or housing while the
shaft is rotated through 360˚ will reveal
DRO. (fig. 9f).
80
Initial leakage will generally occur in the area that shows little or no
seal wear. This is because of inadequate lip contact. But as the worn
side is hardened from excess pressure and heat, it may crack and
cause additional leakage.
Corrective Actions
Check the shaft-to-bore alignment, and adjust it. Inspect the shaft and
bore before installing the replacement seal. Replace worn bearings.
Lip Wear
Look for clues in the sealing member of the seal. A small cut, nick
or abrasives continually laying at lip/shaft interface could be the source
of the leak. But if everything looks intact, it’s time to look at the wear
pattern of the lip (fig. 9g).
Causes
A new seal which has never been installed has a sharp edge at
the contact point. Following a period of normal operation, the lip’s
sharp edge will be flattened some by normal wear. If the lip has
been substantially worn away, the seal may not be getting enough
lubrication, the shaft may be corroded, the vent in the lube system
may be blocked, or the finish too rough. Extreme wear could also be
caused by shaft-whip (DRO). It could also be caused by excess
pressure or by misalignment (STBM).
A
B
Corrective Actions
Check the shaft-to-bore alignment. Correct the alignment. Provide
proper lube for the seal if there isn’t enough. Repair the shaft if the
shaft is not properly finished. Use a seal designed to exclude abrasive
contaminants if there is an abrasive build-up. Clean and open vents
that are blocked to reduce pressure. If conditions warrant, consider
using a seal designed for high pressure.
C
The illustration above compares
the lip on a new seal (A) to one
with normal wear (B) and one with
excessive wear (C) (fig. 9g).
Outer Case Damage
A “curled” or rolled edge of the seal metal case indicates damage.
The damaged zone may feel rough.
Causes
The housing bore may have a square corner or not have had a proper
lead-in chamfer. Without it, the seal may bind on insertion. This can
cause cocking or create a beveled or rolled end for part of its circumference. It’s also possible that the bore diameter and tolerance are
incorrect.
Corrective Actions
Insure that the bore does not start with a square corner. Per industry
standard, it should have a 15˚-30˚ angle and the corners should be
smooth and free of burrs. Confirm that the bore size is correct for the
seal.
9
Examining the Outer Shell
No Chamfer
The beveled edge (chamfer) on the
leading edge of the bore provides a ramp
for starting the seal straight. Without it,
it is virtually impossible to get the seal
installed correctly. A 15˚-30˚ angle, clean
and burr free, is recommended. (fig. 9h).
81
Out-of-Round Shaft
Early lip leakage is also a symptom that the shaft is out-of-round
(fig. 9i). Industry specifications are listed in the 457010 SKF Handbook
of Seals.
Causes
Inspect the shaft to see if it is out-of-round. Flat spots on the shaft
can also cause early lip leakage.
An out-of-round shaft can also
cause seal leakage (fig. 9i).
Corrective Actions
Check the shaft’s “roundness” by measuring with a micrometer in
three equally spaced points circumferentially near the location of the
seal. Tolerances should be within the allowable range for the shaft size.
Be sure the shaft is carbon or stainless steel, finished 8 to 17
micro-inch Ra (0.20μm to 0.43μm), with no machine lead. One
solution is to remove and resize or reshape the shaft first. Then
repair the shaft with either a Speedi-Sleeve or an SKF Large
Diameter Wear Sleeve.
Gar ter Spring Damage
Garter spring problems are easy to spot. The spring may be loose, or
out of the seal. The spring may pop out and damage the mechanical
components. Or, the spring may be missing (fig. 9j).
Causes
Maybe the spring was never installed in the seal. Perhaps it was
dislodged from the seal prior to installation. Or maybe too much
shock was transmitted to the seal during installation.
Garter spring problems are visible
and easy to spot (fig 9j).
Corrective Actions
The only solution is to install a replacement seal. But first, check
the spring on the new seal. It could have become dislodged during
packaging or shipment. If so, install the spring into the seal. Use
correct mounting tools and follow correct installation procedures.
Be sure to apply press fit force uniformly.
82
Cut Seal Lip
Ever-so-slight seal leakage is evidence that there may be a small nick
or cut in the sealing lip (fig. 9k).
Causes
It may have been caused by a burr on the keyway, spline or shaft end.
Corrective Actions
Follow these steps to correct and prevent cuts on the seal lip:
• Use a deburring tool or emery cloth to remove any burrs. Use
correct mounting tools to protect the seal lip from sharp edges. Be
sure to tape the keyway or spline. Handle seals carefully. Keep seals
packaged during storage or while in transit.
A nicked seal lip also causes lip
leakage (fig. 9k).
Lube Breakdown
Sludge or varnish-like deposits on the seal lip and/or shaft are
symptoms of lube breakdown (fig. 9l).
Causes
Sometimes heat is high enough to break down the oil, but not enough
to harden the lip. In this case, sludge accumulates and is deposited on
the seal lip.
Corrective Actions
Reduce operating temperature if possible, or use a seal designed
for high temperatures (fluoroelastomer type). Be sure to use proper
lubricant for the seal. It also helps to change the oil regularly.
Sludge deposits on the seal lip
indicate lube breakdown (fig. 9l).
9
Heat Checking
Heat checking or cracking is another common sealing problem.
This may be evidenced by a hardened seal lip or fine cracks that show
up in the seal lip surface (fig. 9m).
Causes
These problems with the seal may be caused by an operating
temperature greater than the lip material maximum. Other
reasons for heat cracking are excessive surface speeds or insufficient
lubrication at the seal lip.
Corrective Actions
Fine cracks in the seal lip are
visible signs of excess heat or
pressure (fig. 9m).
One possible solution is to reduce the temperature or select a seal
material with a higher temperature range. In the other cases, change
the lip material to one that is compatible with the lube or provide
proper lube for the seal. For high pressure applications, be sure to
use a seal designed for that purpose, such as CRWA5.
83
Pressure Blow-Out
Another visible seal problem is a ruptured or inverted seal lip. Either
problem results in lip leakage (fig. 9n).
Causes
Pressures exceeding seal design limitations can cause seal rupture,
inverted lips and resultant lip leakage.
Corrective Actions
Too much pressure can
rupture the seal lip (fig. 9n).
Check the seal cavity for excess pressure. Provide vents to reduce pressure, or use a seal designed for high pressure applications (CRWA5).
Pressure Lip Wear
Signs of excessive pressure include extreme lip wear and lip leakage.
Causes
Excess pressure can crush the lip against the shaft. Heavy friction will
eventually force the garter spring through the lip. Excess pressure can
blow the lip completely off (Fig. 9o).
Corrective Actions
Extreme lip wear (B) is a sign of
excess pressure. Note the lip with
pressure (A) (fig. 9o).
We recommend two ways to prevent seal failure caused by excessive
pressure. First, check the air vents to be sure they are clean. If not
open them to reduce pressure. Dirt or paint may block proper air flow.
Second, if the system is clean, try using a medium pressure seal such
as the CRW5 and CRWA5. Make sure the system operating parameters are within the seal’s capability.
Chemical Swelling
A swollen, distorted appearance of the seal rubber element combined
with a “soft” feel can indicate incompatibility between the lip compound
and the media being retained or excluded.
Causes
Chemical swelling
Incompatibility between the lip
material and the operating media,
including lubricants, can produce
major swelling of the seal material.
Above is a before (1) and after (2)
example of the gross damage
you may see from chemical
incompatibility.(fig. 9p).
84
The rubber is experiencing swell, an increase in volume resulting from
the compound absorbing the attacking media. This displacement of the
rubber molecular structure reduces the physical strength of the rubber
leading to rapid wear and failure. In extreme cases, the rubber may
dissolve completely. With some compounds, heat or other agents can
also be responsible.
Corrective Actions
Consult seal catalogs and investigate to make sure that the selected
seal compound is acceptable for the media and operating conditions.
Sometimes a rubber type can be sensitive to a particular media but
still be adequate in the expected application but in other cases it can
be ruined.
Chapter 9 Review
To take this test, simply place a card or sheet of paper under the first question. After you’ve
read it (and answered it to yourself), slide the paper down below the next question. The
correct answer to the first problem will appear directly to the right of the new question.
1. Premature seal failure can be caused by _________________ .
❑ a. nicks on the bore chamfer
❑ b. improper seal installation
❑ c. shaft-to-bore misalignment
1. D
2. If a seal’s lip shows premature wear _________________ .
❑ a. the seal may not be getting enough lubrication
❑ b. the shaft may be corroded
❑ c. the finish is too rough
2. D
3. A cut lip seal may have been caused by _________________ .
❑ a. a damaged seal housing
❑ b. shaft discoloration
❑ c. coked lube on the shaft
❑ d. a burr on the keyway
3. D
4. Pressures exceeding seal design limitations can cause _________________ .
❑ a. seal rupture
❑ b. inverted lips
❑ c. lubricant leakage
9
4. D
5. Heat checking or cracking is sometimes caused by lack of lubrication.
❑ True ❑ False
5. T
6. The only solution to garter spring damage is to install a replacement seal.
❑ True ❑ False
6. T
7. If high operating temperatures cannot be reduced, fluoroelastomer type seals
(SKF LongLife) can be used because of their higher temperature range.
❑ True ❑ False
7. T
85
Chapter 9 Review (cont...)
8. Garter spring damage requires careful inspection, often necessitating
calling in an “expert.”
❑ True ❑ False
8. F
9. For out-of-round shaft repairs, a Speedi-Sleeve or SKF Large Diameter Wear
Sleeve is often a better solution than shaft removal and reshaping.
❑ True ❑ False
9. F
10. When examining for STBM, the lip area with the least wear indicates
the direction of shaft misalignment.
❑ True ❑ False
10. F
11. When using a wooden workpiece for flush installation of a seal, it is acceptable
to use a steel hammer.
❑ True ❑ False
11. T
12. Because seal I.D. is easy to measure, only three measurements need
to be taken and averaged.
❑ True ❑ False
12. F
13. When determining the cause of a leak, remove the seal immediately and inspect it.
❑ True ❑ False
13. F
14. If there is a history of seal failures for a particular installation, the problem
may not be the seal’s fault.
❑ True ❑ False
14. T
15. A hammer blow without any material to absorb the shock wave can
dislodge the garter spring from its proper operating position.
❑ True ❑ False
15. T
16. A swollen appearance and soft feel to a seal’s rubber element probably indicates
chemical incompatibility with the system media.
❑ True ❑ False
16. T
17. There is no problem installing a seal into a bore without a lead-in chamfer.
❑ True ❑ False
17. F
86
Glossary of Seal Terms
Abrasives – Materials that cause wear,
friction or irritation
Burr – A rough edge on metal or other material
after it has been cast, cut, or drilled.
All-Rubber Seals – A non-metal clad seal made of
rubber commonly used where space limitation and
installation difficulties are a major consideration.
Two basic types of HS all-rubber seals are solid
and split, both require a cover plate for proper
compression and sealing.
Case, Bonded – A design feature of a type of radial
lip seal wherein the heel of the sealing element is
attached to the seal case by an adhesive during the
molding operation.
Auxiliary Lip – See Secondary Lip
Case, Inner – A rigid, cup-shaped component of a
seal assembly, which is placed inside the outer seal
case.
Axial Seal – Applies force along the direction of
the shaft, usually between one moving and one
stationary element. Examples: carbon
face seal, V-Ring.
Case, Outer – The outer thin-wall rigid structure of
the lip-seal assembly which contains the inner case,
the primary-seal ring, the spring parts, and the
secondary seal.
Axial Clamp Split Seal – Made of nitrile, these
compact seals operate against a rotating step or roll
face. Recommended for large diameter applications
where there is the need for a second seal to
exclude dirt.
Case, Seal – A rigid member to which the seal lip
is attached.
Bearing – An anti-friction device that supports,
guides, and reduces friction between fixed and
moving machine parts. Rolling bearings rely on
balls or roller elements riding within raceways on
a thin film of lubricant. Plane or sleeve bearings
use only a lubricant film.
Bi-rotational Seal – A rotary shaft seal which will
seal fluid regardless of direction of shaft rotation.
Bond – The adhesion established by vulcanization
between two cured elastomer surfaces, or between
one cured elastomer surface and one
non-elastomer surface.
Bonded Seal – Design feature of a type of radial
lip seal. The heel of the sealing element is attached
(bonded) to the seal case by an adhesive during the
molding operation.
Bore – See Seal Bore.
Bore-tite – A sealant that fills small bore
imperfections.
Bottom Out – Installation of a seal into a groove
until it reaches the end of possible travel. Additional
force should not be used or damage can result.
Buna-N – See nitrile.
i
Case Width – The total axial width of the seal case.
Cavity, Mold – A single unit or assembly of
contoured parts in which a material, such as an
elastomer, is shaped into a particular configuration.
Cavity, Seal – The annular area between a housing
bore and a shaft, into which a seal is installed.
Chamfer – A surface that has a groove cut in it or
the edge or corner is cut off; beveled.
Cocked – An installation in which the plane of the
outside seal face is not perpendicular to the shaft
axis.
Compound – A substance or material formed
by the combination of two or more otherwise
independent elements.
Contaminants – Foreign matter on the seal
surface.
Contact Pressure – The average pressure exerted
by a seal on a shaft. This pressure is computed
dividing the total lip force by the total lip area. Also
referred to as radial load.
Counterface – The end of a bearing, a washer, a
steel stamping, or even the back of an oil seal shell.
Cover Plate – Metal plate used to compress all
rubber (HS) seals in the bore and hold them
securely.
87
Glossary of Seal Terms (cont...)
Diameter – A straight line segment passing
through the center of a figure, especially of a circle
or a sphere.
End-Play – A measure of axial movement
encountered or allowed, usually in reference to
the shaft on which the seal lip contacts.
Diameter, Trimmed Lip – The lip diameter in the
free state (no spring) developed by knife trimming
the molded portion of the sealing element to form
the contact line.
EP lubes – “Extreme Pressure” lubricants which
contain additives to increase the strength of the
lubricant film. These additives can include sulfur,
chlorine, or phosphorus compounds that can attack
the sealing materials.
Diamond Burnishing – A method of shaft surface
finishing in which the burnishing medium moves
axially.
Double Lip – Use of two sealing elements. One is
usually spring loaded, the other not. However, can
also have two spring loaded lips. Can be opposed
or in same direction.
Duralip - SKF’s special nitrile compound for
extreme abrasion resistance. Recommended
where scale, sand, grit, dirt or other highly
abrasive materials are present.
Duratemp – A special compound based on hydrogenated nitrile (HNBR) Duratemp offers improved
tensile strength and resistance to heat, abrasion,
hardening in hot oil, ozone and weathering effects.
Dynamic Run-Out (DRO) – The amount by which
the shaft does not rotate around its true center.
Dynamic Seal – A seal which has rotating,
oscillating, or reciprocating motion between it and
its mating surface, in contrast to a stationary-type
seal, such as a gasket.
DIN – “Deutcshes Institute fur Normung” German
standards organization that is a member of
International Standards Organization (ISO).
Eccentricity, Lip I.D. – See: variation, radial wall.
Eccentricity, Shaft – The radial distance which the
geometric center of a shaft is displaced from the
axis of shaft rotation.
Elastomer (Lip Material) – An elastic rubberlike
substance, such as natural or synthetic rubber.
88
Exclusion – The prevention of dirt, water and
contaminants from entering the bearing cavity.
Flange – A protruding rim or edge used to
strengthen an object or hold it in place.
Flinger – Synonym: slinger.
Fluid Side – Side of the seal which normally
faces the fluid being sealed.
Fluoroelastomer – A saturated polymer in which
hydrogen atoms have been replaced with fluorine.
It is characterized by excellent chemical and heat
resistance.
FPM – Feet per minute; used as a measure of
shaft speed instead of rpm. To convert rpm into
fpm, use the formula: .262 x rpm x shaft diameter
(inches) = fpm.
Garter Spring – A Helically coiled spring wire with
its ends connected to form a ring. It is used for
maintaining a sealing surface between the sealing
element and a sealing surface.
Glass Bead Blasting – A method of shaft surface
finishing in which the shaft surface dimples.
Grinding Wheel-To-Shaft-Ratio – A number ratio
between grinding wheel rpm and shaft rpm. The
whole number is proportionate to the number of
lead grooves formed in the shaft. For example, at
a 2 to 1 ratio, one groove on the grinding wheel
will form two lead grooves on the shaft surface.
Groove, Spring – A depression formed in the
head of the section of the seal. It is generally
semicircular in form and serves to accommodate
and locate the garter spring.
Hardness – The resistance to indentation.
Measured by the relative resistance of the
material to the indentor point of a standard
diameter test instrument. The Shore A scale is
commonly used for rubber materials. For steel
a Rockwell Hardness Tester is used with the
Rockwell or Brinnel hardness scale.
Helical – Shaped like a helix; a three-dimensional
curve that lies on a cylinder or cone and cuts the
elements at a constant angle; a spiral form.
Keyway – A notch cut axially into the O.D. of a
shaft. Used with a key and notched component
(gear, drive, etc.) to radially lock the component
onto the shaft.
Helix Seal – An elastomeric hydrodynamic lip
seal having helical ribs on the outside lip surface.
Large Diameter Seals – Seals that fit shaft 8”
(200mm) in diameter and larger.
Housing – A rigid structure which supports the
seal assembly with respect to the shaft.
Lip, Dirt – See Secondary Lip.
Lip, Dust – See Secondary Lip.
Housing Bore – A cylindrical surface which
mates with the outside surface of the seal outer
care (also referred to as a seal bore).
Lip, Molded – A type of seal lip which requires
no trimming to form the contact line.
Hydraulic – Use of fluid pressure to perform
work. Examples include cylinders, accumulators,
motors, motor drives and pumps.
LongLife Seal – SKF seal utilizing premium
high performance fluoroelastomer materials
for extended life service against high speed,
heat and chemical attack.
Hydraulic/Pneumatic Seals – Seals used to
contain fluid or gas pressure and protect them
from contamination.
Hydrodynamic Seal – A dynamic sealing device
which utilizes the viscous shear and inertia forces
of the fluid; imparted by a helically grooved or
ribbed seal lip, to generate a pressure differential
that opposed fluid flow.
Hydroseal – A sealing system having helically
disposed elements formed on the shaft surface.
HDDF – SKF Heavy Duty Dual Face axial seal.
I.D. – See Seal, Inside Diameter.
Inclusion – Foreign material included in the seal
material.
Interface – The region between the static
and dynamic sealing surfaces in which there is
contact, or which experiences the closest
approach and effects the primary seal.
ii
ISO – International Standards Organization.
This is the international organization which sets
standards for quality excellence in manufacturing
organizations, service industries, and small
companies. Sets tolerance specifications for
metric systems.
Lubricant – Any of various materials, such as
grease, or machine oil, that reduces friction when
applied as a coating to remove parts; lube.
Machine Lead – Spiral grooves similar to a
screw thread on a shaft surface. May be caused
by improper shaft finishing. May result in early
seal leakage.
Metal Clad Seals – Seals using a metal case
or housing.
Metallize – Addition of new metal to fill grooves
or nicks on worn shafts.
Misalignment – Physical displacement of
the shaft centerline to theoretical drive center.
Can be fixed (shaft to bore misalignment)
or variable (dynamic run-out).
M/S – Meters per second. Calculate as (shaft
diameter (mm) x RPM x .001 x 3.142) /60
89
MPM – Meters per minute. Calculate as shaft
diameter (mm) x RPM x .001 x 3.142
Nick – A void created in the seal material after
molding.
Nitrile – A general term for the co-polymer of
butadiene and acrylonitrile. ASTM class NBR.
Non-Spring loaded – Seal without a spring.
Applies radial force only through elasticity of the
rubber lip and interference.
Non-Synthetic – Before synthetic materials were
developed, naturally occurring materials were used.
Leather was the sealing element commonly found
in earlier seals. Felt was also extensively used for
grease and dust seals.
Oil Resistance – The measure of an elastomer’s
ability to withstand the deteriorating effect of
lubricant on the mechanical properties.
O-Ring – A toroidal shaped seal, commonly round.
Variations are square, lobed or rectangular.
Out-Of-Round, Shaft – The deviation of the shaft
cross section from a true circle.
O.D. – See Seal, Outside Diameter.
Paper Polishing – Finishing the surface of a shaft
with abrasive paper.
Parabolic – Like a parabola; a plane curve formed
by the locus of points equidistant from a fixed line
and a fixed point not on the line.
Plunge Ground – The surface texture of shaft or
wear sleeve produced by presenting the grinding
wheel perpendicular to the rotating shaft without
axial motion.
Polyacrylate - A type of elastomer characterized
by an unsaturated chain and being a copolymer
of alkyl acrylate and some other monomer such
as chloroethyl vinyl ether or vinyl chloroacetate.
ASTM class ACM.
90
Press Fit – Retention force achieved by installing
an element whose contact diameter is greater (or
less) than its mating surface.
Primary Lip – The flexible elastomeric component
of a seal lip which contacts the rotating surface,
performing the main sealing function.
psi – Pounds per square inch. Measure of
pressure for fluids and gases.
PTFE – Polytetrafluoroethylene. A thermoplastic
polymer developed by Dupont with outstanding
heat and chemical resistance.
Radial Seal – A seal which exerts radial sealing
pressure in order to retain fluids and/or exclude
foreign matter.
Radius – A line segment that joins the center
of a circle with any point on its circumference.
Retention – To retain lubricants or pressure
within the bearing cavity.
Retention Seals – These seals are often springloaded to retain lubricants or confine pressure in
the bearing cavity.
Roller Burnishing – A method of shaft surface
finishing in which the surface peaks caused by
lathe cutting appear to flatten. The original lead
grooves are compressed and not removed.
Roto preening – A method of shaft surface
finishing in which the shaft surface dimples and
kerfs at one side of the depression.
Run-In – The period of initial operation during
which the seal-lip wear rate in greatest and the
contact surface is developed. Synonym:
bedding-in.
Run-Out – That run-out to which the seal lip is
subjected due to the outside diameter of the shaft
not rotating in a true circle. Usually expressed as
TIR (Total Indicator Reading).
Ra – Measure of surface roughness average
of all peaks and valleys from the main line
within one cut-off (normally .030” or .76mm)
of measurement.
RMA – Rubber Manufacturers Association.
Sets inch standards.
RPM – Revolutions per minute.
Scoring – A type of wear in which the
working surface of the shaft is grooved.
Scotseal – “Self Contained Oil Type.” An SKF
seal which integrates multiple rubber sealing
elements within a housing which provides
a running surface.
Seal Bore – The diameter of the hole in the
housing into which the seal is fitted.
Seal, Head Section – The portion of a lip
seal which is generally defined by the inside
and outside lip surfaces and the spring
groove.
Seal, Inside Diameter (I.D.) – The internal
diameter of a lip seal assembly. Usually the
inside diameter of the inner seal case.
Seal Interference – The difference between
the seal lip and shaft diameters.
Seal, Outside Diameter (O.D.) – The external
diameter of a lip seal assembly. Usually the
outside diameter of the outer seal case.
Seal Width – The overall axial dimension of
the lip seal assembly. Normally the total width
measurement of the outer seal case.
Sealing Element – The normal flexible
elastomeric component of a lip seal assembly
which rides against the shaft.
Secondary Lip – A short, non-spring loaded
lip which is located at the outside seal face
of a radial lip seal. Used to exclude
contaminants.
iii
Section, Head – The portion of a lip seal
which is generally defined by the inside and
outside lip surfaces and the spring groove.
Shaft Diameter – The outside diameter of
the shaft at the location where the seal is
mounted.
Shaft Finish – The relative roughness,
usually expressed in micro inches, of the
outside diameter of the shaft. The smaller
the number, the smoother the finish.
Shaft Hardness – Under normal conditions,
the portion of the shaft contacted by the seal
should be hardened to Rockwell C30
minimum. There is no conclusive evidence
that hardening above this will increase the
wear resistance of the shaft except under
extreme abrasive conditions. Where the shaft
is liable to be nicked in handling previous to
assembly, it is recommended that it be
hardened to Rockwell C45 minimum in order
to prevent against being permanently
damaged during assembly.
Shaft Seal Nomenclature – The basic seal
components including: Outer Shell (Case),
Inner Shell (Case), Sealing Element, Primary
Lip, Secondary (Auxiliary) Lip and the Garter
Spring. Each perform a particular function.
Shaft Seal – Generally considered to be a lip
seal or an oil seal. A broad definition could
include any sealing device mounted on a shaft
or sealing shaft.
Shaft Surface Texture – A prime factor in
the proper functioning of a lip seal The surface
roughness should be specified as 8-17
microinch (0.20μm-0.43μm) Ra with no
machine lead. The best known method to
date for obtaining this roughness is plunge
grinding.
Shell, Inner (Case, Inner) – A rigid,
cup-shaped component of a seal assembly,
which is placed inside the outer seal shell. It
can function as a reinforcing member, shield,
spring retainer or lip-clamping device.
91
Shell, Outer (Case, Outer) – The outer,
cup-shaped, rigid structure of the lip assembly.
Acts as a protective cover for the head of the
sealing element.
Silicone – A type of elastomer having a basic
polymer of dimethyl polysilozane, with various
attached vinyl or pheyl groups. (ASTM class VMQ)
Single Lip – Seal element utilizing one contact
point, with or without springs.
Sinusoidal – Describing an alternative wave form
centered on a fixed line.
Sirvene – SKF’s tradename for synthetic rubber.
Slinger – A washer-like device used for imparting
radial momentum to a liquid order too keep the
latter away from the sealing interface. Often
incorporated into a wear sleeve.
Small Diameter Seals – Seals that fit shafts
ranging from .110” to 12.5” (2.8mm to 317.5mm)
in diameter.
Solid Seals – Continuous seals without a split.
Spark Out – When the grinding wheel is allowed
to run until there are no more sparks flying from
the wheel.
Speedi-Sleeve – The Speedi-Sleeve is a highly
engineered, precision part of the finest 300 series
stainless steel. Its surface is factory finished to
10-20 micro inch Ra (.25-.50 micro meter), with
no machine lead, and requires no expensive preparation or machining before installation.
Spindle – Slots of positive or negative alternating
shapes used to connect two elements, one usually
drives the other.
Split Seal – A seal which has its primary sealing
element split, approximately parallel with the shaft
axial centerline. Typically used where conventional
installation methods are impractical.
92
Spring-Loaded – The design of most oil seals in
which a spring is incorporated to provide a uniform
load at the seal contact line-shaft surface junction.
Spring-Lock – A sealing lip design that extends
over and surrounds most of the garter spring’s
diameter.
Spring-Kover – A flexible, rubber like covering that
totally enclosed the garter spring.
Spring Position – The axial distance between the
“seal contact line” and the centerline of the spring
groove of a radial lip seal; commonly referred to as
the “R” value.
Static Seal – Seal without a dynamic contact
surface. Example is a refrigerator gasket.
Surface, Contact – The portion of the seal lip
which circumferentially contacts the shaft to form
the seal-shaft interface.
Surface Honing – A cross hatching pattern on the
shaft causing a grooving which tends to act as a
lead, allowing lubricant to escape under the seal lip.
Synthetics – The most popular and versatile lip
sealing element in use today. These include
nitriles, polyacrylates, silicones and fluoroelastomers.
Synthetic Rubber – Synthetic elastomers made by
polymerization of one or more monomers.
STBM – Shaft-to-bore-misalignment. The amount
by which the shaft is off center, with respect to the
bore’s center.
Talysurf – Device used to measure shaft surface
finish.
Test, Accelerated Life – Any set of test conditions
designed to reproduce in a short time the effects
obtained under service conditions.
Test, Bench – A laboratory test procedure in
which the functional operating conditions are
approximated, but the equipment is conventional
laboratory equipment and not necessarily identical
with that in which the product will be used.
Test, Life – A laboratory procedure used to
determine that period of operation which a
component or assembly will operate until it
no longer performs its intended function.
Vulcanizing – An irreversible heat and chemical
treatment process that makes rubber in a seal
more elastic and durable. Used to rejoint
V-rings that were split during installation.
Through Bore – Bore without a diameter
reduction, may have a bearing in line with
a seal.
“WasteWatcher” – An SKF program designed
to consolidate seal stocking units in relation
to their applications to control replacement
inventory and effect cost savings for the user.
Tolerances – Bore and Seal – The bore and
seal tolerances.
Torque – The tendency of a force to produce
rotation about an axis.
Transverse Grinding – A shaft surface
finishing method of which there are two types;
either the grinding medium moves laterally
while the shaft turns, or the wheel rotates in
a fixed position while the shaft turns and
moves laterally.
Tumbled Stone Finishing – A shaft surface
finishing method in which a uniform shaft
appearance is produced.
iv
Waveseal – The SKF Waveseal is a smooth
lip, bi-rotational hydrodynamic radial lip seal.
A shaft seal that pumps lubricant back in the
sump while sealing out contaminants – no
matter which way the shaft is turning.
Wear Sleeve – A replaceable metal ring.
Generally used in assemblies to eliminate
expensive shaft replacement caused by
grooving that may occur at the seal shaft
interface.
Width – See Seal Width.
Underlip – The area under the seal lip.
Unitized Seal – A seal assembly in which
all components necessary for accomplishing
the sealing function are retained in a single
package.
Variation, Radial Wall – The difference
between the minimum and maximum radial
wall dimensions when measured around 360
of the seal lip.
Vibration, Torsional – A vibration which has
a circumferential or angular direction. It is
often generated by a stick-slip action between
mating seal surfaces.
V-Ring Seal – A versatile all-rubber seal that
mounts directly on the shaft by hand and is
then sealed axially against a counterface,
housing bearing race or similar surface.
Functions by “slinger” or deflector action.
93
Final Exam
Congratulations. You have completed the Shaft Seals Industrial Self-Study Program.
Now you are ready to test your knowledge about SKF seals, Speedi-Sleeves and Scotseals
in this Final Review.
First, turn to the last page of this study guide. Remove the Final Review answer sheet by
tearing it out carefully along the perforated edge.
Begin the test. Be sure to answer every question; unanswered questions will be graded
as incorrect.
When you have finished the test, fold your answer sheet as indicated, with the return
address on the outside. Staple it closed; no envelope is required. Be sure to attach the
proper postage, and mail your answer sheet to SKF.
If you score 85% or more, you will receive a Cer tificate of Merit f rom SKF.
Please allow at least four weeks for grading.
If you have a seal problem that cannot be answered through this study guide, contact
your SKF representative. He’s backed by a full crew of technicians—product managers,
engineers and service personnel—who will gladly provide the assistance you need.
When you have a question, call SKF toll-free: 1-800-882-0008.
1 . A shaft seal is a barrier designed to retain lubricants and _________________ .
❑ a. confine pressure
❑ b. exclude dirt
❑ c. separate fluids
2. Selecting the right seal depends on application parameters, including
_________________ .
❑ a. shaft speed
❑ b. fluid compatibility
❑ c. operating pressure
3. When split seals are used in multiples, a _________________ is often used to separate
the seals and provide extra lubrication between them.
❑ a. horizontal shaft
❑ b. slotted washer
❑ c. control wire
❑ d. butt joint
4. Premature seal failure can be caused by _________________ .
❑ a. nicks on the bore chamfer
❑ b. improper seal installation
❑ c. shaft-to-bore misalignment
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5. When considering seals and wear sleeves for a large diameter shaft, it is possible to
_________________ .
❑ a. machine the shaft to a reduced diameter for
use with the wear sleeve and original size seal.
❑ b. Apply the .094” thick (2.4mm) wear sleeve and
use a larger sized seal.
v
6. _________________ is the most popular material for the majority of sealing
applications today.
❑ a. Leather
❑ b. Felt
❑ c. Nitrile
❑ d. Silicone
7. Waveseals _________________ .
❑ a. generate less heat
❑ b. reduce shaft wear
❑ c. provide greater lip lubricant
8. The seal is ready to be installed in the bore once the shaft and bore have been
checked and cleaned, and the seal has been _________________ .
❑ a. pre-lubricated
❑ b. split
❑ c. vulcanized
9. Two metal clad seals (Type HDS), back to back or in tandem,
❑ a. provide extra-duty sealing
❑ b. are less expensive than a double seal
❑ c. install easier than a double seal
10. _________________ seals are the basic type large diameter seals.
❑ a. HDS metal clad (all-rubber)
❑ b. HS non-metal clad (all-rubber)
❑ c. Both of the above
❑ d. None of the above
11. Type _________________ has two opposing sealing elements in a single shell,
making it ideal for separating two fluids in applications where two seals are impractical.
❑ a. HDSA
❑ b. HDSD
95
12. A cocked seal can cause a seal lip to _________________ .
❑ a. leak
❑ b. groove the shaft
13. If a seal’s lip shows premature wear _________________ .
❑ a. the seal may not be getting enough lubrication
❑ b. the shaft may be corroded
❑ c. the finish is too rough
14. The flange allows the Speedi-Sleeve to be _________________ eliminating
sleeve distortion.
❑ a. pushed on
❑ b. pulled on
❑ c. either of the above
15. When heat is enough to break down the oil, but not enough to harden the lip, sludge
accumulates and deposits on the _________________ .
❑ a. garter spring
❑ b. bore
❑ c. seal lip
16. Popular sealing lip synthetics in use today include _________________ .
❑ a. nitriles
❑ b. fluoroelastomers
❑ c. fluorocarbons
17. A cut lip seal may have been caused by _________________ .
❑ a. a damaged seal housing
❑ b. shaft discoloration
❑ c. a coked lube on the shaft
❑ d. a burr on the keyway
18. _________________, required by all HS type seals, provide axial compression
and supplement radial press-fit to ensure leakproof seals.
❑ a. Spring-Lock
❑ b. Spring-Kover
❑ c. Cover plates
96
19. _________________ are dual face mechanical seals used where both positive
lubrication and dirt exclusion are required.
❑ a. Waveseals
❑ b. V-Rings
❑ c. HDDF seals
❑ d. Retention seals
vi
20. Selecting the right seal for a particular application depends on _________________ .
❑ a. size and speed
❑ b. pressure and temperature
❑ c. fluid compatibility
21. The V-Ring is an all-rubber seal that _________________ .
❑ a. mounts directly on the shaft by hand
❑ b. is sealed axially against a counterface, housing bearing race
or similar surface
❑ c. acts like a mechanical face seal, radial lip seal or slinger
22. Installation of a Large Diameter Wear Sleeve without any
machining _________________ the effective shaft diameter.
❑ a. reduces
❑ b. increases
❑ c. will never change
23. Pressures exceeding seal design limitations can cause _________________ .
❑ a. seal rupture
❑ b. inverted lips
❑ c. lubricant leakage
24. Heavy-duty mechanical seals (HDDF) _________________ .
25. Simultaneous exclusion and retention is best performed with _________________ .
❑ a. a combination of two seals back to back
❑ b. single lip design seals
❑ c. a combination of two seals front to back
❑ d. V-Ring seals
97
26. In _________________ installation, the sealing force of the installation
tool should be applied only in the area over the center of the seal.
❑ a. wooden block
❑ b. arbor press
❑ c. Speedi-Sleeve
27. Using the _________________ method to set the seal perpendicular
to the shaft when installing a “through” bore, apply pressure
through a steel plate or plug larger than bore diameter.
❑ a. wooden block
❑ b. arbor press
❑ c. Speedi-Sleeve
28. _________________ refers to the outside diameter of the shaft at the location where
the seal is mounted.
❑ a. Size bore
❑ b. Seal I.D.
❑ c. Seal width
❑ d. Shaft diameter
29. SKF’s Large Diameter Wear Sleeves _________________ .
❑ a. repair damaged shafts 8” (203mm) and larger.
❑ b. are built for heavy-duty applications
❑ c. provide positive sealing surfaces and reinforced protection
30. Advantages of polyacrylates include _________________ .
❑ a. good compatibility with most oils
❑ b. high resistance of oxidation and ozone
❑ c. better compatibility with higher temperatures than nitrile
31. _________________ are designed for heated, slip-fit operation.
❑ a. Speedi-Sleeves
❑ b. Large Diameter Wear Sleeves
32. Press-fitting tools should have an outside diameter approximately _________________
the bore size.
❑ a. .010” (.254mm) smaller than
❑ b. .010” (.254mm) larger than
❑ c. equal to
98
33. A hammer blow without any material to absorb the shock wave _________________ .
❑ a. may interfere with the action of the seal lip
❑ b. can dislodge the garter spring from its proper operating position
vii
34. To assure a smooth sealing surface, the shaft should be ground
with _________________ rpm ratios.
❑ a. even number (2 to 1)
❑ b. odd number (3 to 1)
❑ c. mixed number (3.5 to 1)
35. If the same size replacement is not available, _________________ .
❑ a. select a narrower seal
❑ b. select a wider seal
❑ c. select a different lip material
❑ d. either a. or b.
36. Before the invention of nitriles, _________________ was the most
common sealing element.
❑ a. rubber
❑ b. felt
❑ c. leather
❑ d. metal
37. For best seal performance, use a(n) _________________ or soft-face hammer
for seal installation.
❑ a. screwdriver
❑ b. arbor press
❑ c. chisel
❑ d. steel hammer
38. _________________ refers to the amount by which the shaft does
not rotate around the true center.
❑ a. Shaft-to-bore misalignment
❑ b. Dynamic run-out
❑ c. Shaft diameter
39. If the shaft is deeply scored, you should fill the groove with _________________ .
❑ a. powdered metal epoxy type filler
❑ b. non-hardening sealant
❑ c. grease
❑ d. SAE 30 oil
99
40. A sealing lip that is cut, turned back or damaged should be _________________ .
❑ a. repaired
❑ b. replaced
❑ c. cleaned
❑ d. chamfered
41. Advantages of silicone include _________________ .
❑ a. good compatibility with oxidized oils
❑ b. high lubrication absorbency
❑ c. excellent abrasion resistance
❑ d. low cost
42. Seals perform best on Rockwell C30 medium carbon steel (SAE 1035,
1045) or _________________ .
❑ a. stainless steel
❑ b. aluminum
❑ c. bronze
❑ d. zinc
43. The seal is ready to be installed in the bore when _________________ .
❑ a. the shaft and bore have been checked and cleaned
❑ b. the seal has been pre-lubricated
44. The wrong installation tool can _________________ .
❑ a. cut the seal lip
❑ b. damage the seal case
❑ c. distort the seal
45. Proper Speedi-Sleeve installation requires that _________________ measurement(s)
be taken.
❑ a. four
❑ b. three
❑ c. two
❑ d. one
46. The _________________ is a smooth lip, bi-rotational hydrodynamic
radial lip seal that pumps lubricant back in to the sump while
sealing out contaminants.
❑ a. V-Ring
❑ b. metal clad seal
❑ c. Waveseal
100
47. _________________ seals have three sealing lips: one primary lip
to keep oil in, two secondary lips to keep dirt out.
❑ a. Scotseal oil bath
❑ b. Scotseal Plus oil bath
viii
48. _________________ seals can be installed by hand, using no more
than common shop tools if any at all.
❑ a. Scotseal oil bath
❑ b. Scotseal Plus oil bath
49. If high operating temperatures cannot be reduced, _________________ type seals
(LongLife) can be used because of their higher temperature range.
❑ a. nitrile
❑ b. large diameter
❑ c. fluoroelastomer
50. To help ensure proper seal performance, the _________________ .
❑ a. entrance edge should be chamfered or rounded
❑ b. surface finish should be 8-17 micro inches (.20-.43 micro meter)
❑ c. shaft surface should have no machine lead
51. _________________ is an acceptable sealing lip material substitute for nitrile.
❑ a. Leather
❑ b. Felt
❑ c. Another nitrile
52. On some seals, SKF applies a coating of Bore-tite to the _________________ which
fills minor bore imperfections.
❑ a. I.D.
❑ b. O.D.
53. Speedi-Sleeves provide a _________________ that is superior to most original
shaft material.
❑ a. sealing surface
❑ b. stainless steel construction
101
54. If a shaft is lightly grooved but does not require filling, _________________ before
installing the Speedi-Sleeve.
❑ a. apply a light layer of nonhardening sealant
❑ b. apply a light layer of powdered metal epoxy type filler
❑ c. apply a light layer of cement
55. The _________________ should be smooth enough to prevent excessive seal
wear, but “rough” enough to form lubricant holding pockets.
❑ a. inside corner of the bore
❑ b. bore center
❑ c. shaft surface
❑ d. both a. and b.
56. The recommended method for obtaining an optimum shaft finish is
_________________ .
❑ a. paper polishing
❑ b. roto preening
❑ c. plunge grinding
❑ d. diamond burnishing
57. _________________ is a lip material for the majority of sealing applications today.
❑ a. LongLife fluoroelastomer
❑ b. Nitrile
58. Seals which are to be flush with the outside of the housing can be pressed in
with a _________________ .
❑ a. drift
❑ b. punch
❑ c. block of wood
❑ d. chisel
59. Typical radial seal applications include _________________ .
❑ a. gearboxes
❑ b. motors
❑ c. pumps
60. HS all-rubber _________________ may be placed around the shaft, connected and
pushed into the seal bore.
❑ a. split seals
❑ b. solid seals
102
61. A combination seal or a double lip seal will always do a better job than a single lip
design.
❑ True ❑ False
ix
62. Roto preening is recommended to dress the shaft and remove lead introduced during
the machine operation.
❑ True ❑ False
63. The only solution to garter spring damage is to install a replacement seal.
❑ True ❑ False
64. The best prelube to use is the lubricant being retained by the seal.
❑ True ❑ False
65. When determining the cause of a leak, remove the seal immediately and inspect it.
❑ True ❑ False
66. For very severe conditions, SKF’s HDDF seals resist abrasives that cause other
seals to fail
❑ True ❑ False
67. When a Speedi-Sleeve is used to repair a damaged shaft, it is inexpensive and
requires little machine downtime.
❑ True ❑ False
68. A cocked seal is perpendicular to the shaft and bore.
❑ True ❑ False
69. Waveseals (CRW5 and CRWA5) perform better than conventional lip seal designs
in pressure applications, and can be used to replace some mechanical seals.
❑ True ❑ False
70. Substitute lip material will extend a seal’s life, no matter which material is chosen.
❑ True ❑ False
71. If there is a history of seal failures for a particular installation, the problem may not
be the seal’s fault.
❑ True ❑ False
72. Spiral grooves (machine lead) may promote seal leakage.
❑ True ❑ False
103
73. More bearings fail from the entrance of foreign material than from loss of lubricant.
❑ True ❑ False
74. Bore material must be metallurgically compatible with the seal type that is used.
❑ True ❑ False
75. When examining for STBM, the lip area with the least wear indicates the direction of
shaft misalignment.
❑ True ❑ False
76. Axial clamp seals are recommended for large diameter applications where there is a
need for two seals but room for one, as in steel and paper mills or logging operations.
❑ True ❑ False
77. When using a wooden workpiece for flush installation of a seal, it is acceptable to use
a steel hammer.
❑ True ❑ False
78. A direct blow on one side of the seal distorts the shell and can cause the lip to be
pressed against the shaft.
❑ True ❑ False
79. Speedi-Sleeve’s wall is so thin that the original size seal can still be used.
❑ True ❑ False
80. Revolutions per minute (rpm) is generally a better indication of seal performance than
feet per minute (fpm).
❑ True ❑ False
81. Shaft and bore diameters should match those specified for the seal selected.
❑ True ❑ False
82. SKF’s “WasteWatcher” seal inventory control system helps control costs of replacement seals.
❑ True ❑ False
83. The overall axial dimension of the lip seal assembly is called seal width.
❑ True ❑ False
84. Garter spring damage requires careful inspection, often necessitating
calling in an “expert.”
❑ True ❑ False
104
85. Imperfections such as surface burrs, nicks or rough spots on the shaft surface
can damage the lip as it slides on the shaft.
❑ True ❑ False
x
86. The more pressure you apply to a seal, the greater the friction heat and
faster the shaft wear.
❑ True ❑ False
87. The temperature of the lubricant being retained is the only temperature reading
critical to seal selection.
❑ True ❑ False
88. Type HDSD seal has two opposing elements in a single shell, making it ideal
for separating two fluids in applications where two seals are practical.
❑ True ❑ False
89. Applications for SKF’s LongLife fluoroelastomers are limited to standard lubricants.
❑ True ❑ False
90. Speedi-Sleeve’s stainless steel construction provides a surface that can outlast
the original shaft material
❑ True ❑ False
91. In SKF’s single lip vs. double lip test, the single lip outlasted the double lip by
nearly 1000 hours.
❑ True ❑ False
92. The heavy-duty DF seal has a special retainer to hold the two sealing ring faces
together for protection against damage or contamination.
❑ True ❑ False
93. For out-of-round shaft repairs, a Speedi-Sleeve or SKF Large Diameter Wear
Sleeve is often a better solution than shaft removal and reshaping.
❑ True ❑ False
94. The V-Ring’s elastic body adheres to the rotating shaft while the actual sealing
occurs at the point of contact between the lip and the counterface.
❑ True ❑ False
95. More than one Speedi-Sleeve size is usually required for each seal application.
❑ True ❑ False
105
96. Ferrous and other commonly used metallic materials (such as aluminum)
are acceptable bore materials.
❑ True ❑ False
97. The heavy-duty DF seal’s sealing ring and mating ring rotate against each other
at right angles to the shaft to form a leak-proof seal.
❑ True ❑ False
98. When an exact replacement is not available, your best option is substitution
of a similar material and design.
❑ True ❑ False
99. V-Rings must be lubricated for all operating conditions.
❑ True ❑ False
100. The most economic repair option for a worn shaft seal is to install a wear sleeve.
❑ True ❑ False
101. A seal should be pressed into housings with a 15˚-30˚ chamfer.
❑ True ❑ False
102. A seal can have a “swollen” appearance and still be acceptable with the system
media.
❑ True ❑ False
106
FINAL REVIEW
Fleet Edition
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State:
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑A
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
❑B
(Revised 2005)
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑C
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
❑D
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.
65.
66.
67.
68.
❑A ❑B
❑A ❑B
❑A ❑B
❑A ❑B
❑A ❑B
❑A ❑B
❑A ❑B
❑A ❑B
❑A ❑B
❑A ❑B
❑A ❑B
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑C ❑D
❑C ❑D
❑C ❑D
❑C ❑D
❑C ❑D
❑C ❑D
❑C ❑D
❑C ❑D
❑C ❑D
❑C ❑D
❑C ❑D
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
Zip:
69.
70.
71.
72.
73.
74.
75.
76.
77.
78.
79.
80.
81.
82.
83.
84.
85.
86.
87.
88.
89.
90.
91.
92.
93.
94.
95.
96.
97.
98.
99.
100.
101.
102.
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ True
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
❑ False
107
Fold Here
Fold Here
PLACE
STAMP
HERE
Marketing Communications
SKF
Suite 200
890 N. State Street
Elgin, IL 60123
Staple Here
NOTES
NOTES
110
NOTES
111
NOTES
112
SKF
890 North State Street, Suite 200
Elgin, Illinois 60123
1-800-882-0008 (U.S.)
1-866-832-6753 (Canada)
website: www.skf.com
© 2006 SKF Group All Rights Reserved
Printed in the U.S.A. Form No. 457966
(Rev. 07/06)

Industrial seal self study guide

Transcription

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